% Clam AntiVirus: User Manual
%
% Copyright (C) 2016-2018 Cisco Systems, Inc.
% Copyright (C) 2008-2013 Sourcefire, Inc.
% Copyright (C) 2002 - 2007 Tomasz Kojm <tkojm*clamav.net>
% Version 0.2x corrected by Dennis Leeuw <dleeuw*made-it.com>
% Version 0.80 corrected by Tomasz Papszun <tomek*clamav.net>
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% but WITHOUT ANY WARRANTY; without even the implied warranty of
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\huge Clam AntiVirus 0.100.0\\
\huge \emph{User Manual}\\
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\noindent
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ClamAV User Manual,
87d
88d
89d
\copyright \ 2018 Cisco Systems, Inc.
Authors: Tomasz Kojm\\
This document is distributed under the terms of the GNU General
Public License v2.\\
Clam AntiVirus is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
the Free Software Foundation; either version 2 of the License, or
(at your option) any later version.\\
This program is distributed in the hope that it will be useful,
but WITHOUT ANY WARRANTY; without even the implied warranty of
MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
GNU General Public License for more details.\\
You should have received a copy of the GNU General Public License
along with this program; if not, write to the Free Software
Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston,
MA 02110-1301, USA.
\end{boxedminipage}
\vspace{0.3cm}
\noindent
\begin{boxedminipage}[b]{\textwidth}
ClamAV and Clam AntiVirus are trademarks of Cisco Systems, Inc.
\end{boxedminipage}
\newpage
\section{Introduction}
Clam AntiVirus is an open source (GPL) anti-virus toolkit for UNIX,
designed especially for e-mail scanning on mail gateways. It provides
a number of utilities including a flexible and scalable multi-threaded
daemon, a command line scanner and advanced tool for automatic database
updates. The core of the package is an anti-virus engine available in a
form of shared library.
\subsection{Features}
\begin{itemize}
\item{Licensed under the GNU General Public License, Version 2}
\item{POSIX compliant, portable}
\item{Fast scanning}
\item{Supports on-access scanning (Linux only)}
\item{Detects over 1 million viruses, worms and trojans, including
Microsoft Office macro viruses, mobile malware, and other threats}
\item{Built-in bytecode interpreter allows the ClamAV signature writers
to create and distribute very complex detection routines and
remotely enhance the scanner's functionality}
\item{Scans within archives and compressed files (also protects
against archive bombs), built-in support includes:
\begin{itemize}
\item Zip (including SFX)
\item RAR (including SFX)
\item 7Zip
\item ARJ (including SFX)
\item Tar
\item CPIO
\item Gzip
\item Bzip2
\item DMG
\item IMG
\item ISO 9660
\item PKG
\item HFS+ partition
\item HFSX partition
\item APM disk image
\item GPT disk image
\item MBR disk image
\item XAR
\item XZ
\item MS OLE2
\item MS Cabinet Files (including SFX)
\item MS CHM (Compiled HTML)
\item MS SZDD compression format
\item BinHex
\item SIS (SymbianOS packages)
\item AutoIt
\item InstallShield
\end{itemize}}
\item{Supports Portable Executable (32/64-bit) files compressed or obfuscated with:}
\begin{itemize}
\item AsPack
\item UPX
\item FSG
\item Petite
\item PeSpin
\item NsPack
\item wwpack32
\item MEW
\item Upack
\item Y0da Cryptor
\end{itemize}
\item{Supports ELF and Mach-O files (both 32- and 64-bit)}
\item{Supports almost all mail file formats}
\item{Support for other special files/formats includes:}
\begin{itemize}
\item HTML
\item RTF
\item PDF
\item Files encrypted with CryptFF and ScrEnc
\item uuencode
\item TNEF (winmail.dat)
\end{itemize}
\item{Advanced database updater with support for scripted updates,
digital signatures and DNS based database version queries}
\end{itemize}
\subsection{Mailing lists and IRC channel}
If you have a trouble installing or using ClamAV try asking on our mailing
lists. There are four lists available:
\begin{itemize}
\item \textbf{clamav-announce*lists.clamav.net} - info about new versions,
moderated\footnote{Subscribers are not allowed to post to the mailing
list}.
\item \textbf{clamav-users*lists.clamav.net} - user questions
\item \textbf{clamav-devel*lists.clamav.net} - technical discussions
\item \textbf{clamav-virusdb*lists.clamav.net} - database update announcements, moderated
\end{itemize}
\noindent You can subscribe and search the mailing list archives at:
\url{https://www.clamav.net/contact.html#ml}\\
Alternatively you can try asking on the \verb+#clamav+ IRC channel - launch
your favourite irc client and type:
\begin{verbatim}
/server irc.freenode.net
/join #clamav
\end{verbatim}
\subsection{Virus submitting}
If you have got a virus which is not detected by your ClamAV with the latest
databases, please submit the sample at our website:
\begin{center}
\url{https://www.clamav.net/reports/malware}
\end{center}
\section{Base package}
\subsection{Supported platforms}
Clam AntiVirus is regularly tested on:
\begin{itemize}
\item{GNU/Linux}
\item{Solaris}
\item{FreeBSD}
\item{macOS}
\item{Windows}
\end{itemize}
\subsection{Binary packages}
You can find the up-to-date list of binary packages at our website:
\url{https://www.clamav.net/download.html#otherversions}
\section{Installation}
\subsection{Requirements}\label{sec:components}
The following components are required to compile ClamAV under UNIX:
\footnote{For Windows instructions please see win32/README in the
main source code directory.}
\begin{itemize}
\item zlib and zlib-devel packages
\item openssl version 0.9.8 or higher and libssl-devel packages
\item gcc compiler suite (tested with 2.9x, 3.x and 4.x series)\\
\textbf{If you are compiling with higher optimization levels
than the default one (\hbox{-O2} for gcc), be aware that there
have been reports of misoptimizations. The build system of ClamAV
only checks for bugs affecting the default settings, it is your
responsibility to check that your compiler version doesn't
have any bugs.}
\item GNU make (gmake)
\end{itemize}
The following packages are optional but \textbf{highly recommended}:
\begin{itemize}
\item bzip2 and bzip2-devel library
\item libxml2 and libxml2-dev library
\item \verb+check+ unit testing framework \footnote{See section \ref{unit-testing} on how to run the unit tests}.
\end{itemize}
The following packages are optional, but \textbf{required for bytecode JIT support}:
\footnote{if not available ClamAV will fall back to an interpreter}
\begin{itemize}
\item GCC C and C++ compilers (minimum 4.1.3, recommended 4.3.4 or newer)\\
the package for these compilers are usually called: gcc, g++, or gcc-c++.
\footnote{Note that several versions of GCC have bugs when compiling LLVM, see
\url{http://llvm.org/docs/GettingStarted.html#brokengcc} for a
full list.}
\item OSX Xcode versions prior to 5.0 use a g++ compiler frontend (llvm-gcc) that is not
compatible with ClamAV JIT. It is recommended to either compile ClamAV JIT with
clang++ or to compile ClamAV without JIT.
\item A supported CPU for the JIT, either of: X86, X86-64, PowerPC, PowerPC64
\end{itemize}
The following packages are optional, but needed for the JIT unit tests:
\begin{itemize}
\item GNU Make (version 3.79, recommended 3.81)
\item Python (version 2.5.4 or newer), for running the JIT unit tests
\end{itemize}
The following packages are optional, but required for clamsubmit:
\begin{itemize}
\item libcurl-devel library
\item libjson-c-dev library
\end{itemize}
\subsection{Installing on shell account}
To install ClamAV locally on an unprivileged shell account you need not
create any additional users or groups. Assuming your home directory is
\verb+/home/gary+ you should build it as follows:
\begin{verbatim}
$ ./configure --prefix=/home/gary/clamav --disable-clamav
$ make; make install
\end{verbatim}
To test your installation execute:
\begin{verbatim}
$ ~/clamav/bin/freshclam
$ ~/clamav/bin/clamscan ~
\end{verbatim}
The \verb+--disable-clamav+ switch disables the check for existence of
the \emph{clamav} user and group but \verb+clamscan+ would still require an
unprivileged account to work in a superuser mode.
\subsection{Adding new system user and group}
If you are installing ClamAV for the first time, you have to add a new
user and group to your system:
\begin{verbatim}
# groupadd clamav
# useradd -g clamav -s /bin/false -c "Clam AntiVirus" clamav
\end{verbatim}
Consult a system manual if your OS has not \emph{groupadd} and
\emph{useradd} utilities. \textbf{Don't forget to lock access to the
account!}
\subsection{Compilation of base package}
Once you have created the clamav user and group, please extract the archive:
\begin{verbatim}
$ zcat clamav-x.yz.tar.gz | tar xvf -
$ cd clamav-x.yz
\end{verbatim}
Assuming you want to install the configuration files in /etc, configure
and build the software as follows:
\begin{verbatim}
$ ./configure --sysconfdir=/etc
$ make
$ su -c "make install"
\end{verbatim}
In the last step the software is installed into the /usr/local directory
and the config files into /etc. \textbf{WARNING: Never enable the SUID
or SGID bits for Clam AntiVirus binaries.}
\subsection{Compilation with clamav-milter enabled}
libmilter and its development files are required. To enable clamav-milter,
configure ClamAV with
\begin{verbatim}
$ ./configure --enable-milter
\end{verbatim}
See section /ref{sec:clamavmilter} for more details on clamav-milter.
\subsection{Using the system LLVM}
Some problems have been reported when compiling ClamAV's built-in LLVM with recent
C++ compiler releases. These problems may be avoided by installing and using
an external LLVM system library. To configure ClamAV to use LLVM that is installed
as a system library instead of the built-in LLVM JIT, use following:
\begin{verbatim}
$ ./configure --with-system-llvm=/myllvm/bin/llvm-config
$ make
$ sudo make install
\end{verbatim}
The argument to \verb+--with-system-llvm+ is optional, indicating the path name of
the LLVM configuration utility (llvm-config). With no argument to \verb+--with-system-llvm+,
\verb+./configure+ will search for LLVM in /usr/local/ and then /usr.
\\\\
Recommended versions of LLVM are 3.2, 3.3, 3.4, 3.5, and 3.6. Some installations have
reported problems using earlier LLVM versions. Versions of LLVM beyond 3.6 are not
currently supported in ClamAV.
\subsection{Running unit tests}\label{unit-testing}
ClamAV includes unit tests that allow you to test that the compiled binaries work correctly on your platform.
\\\\
The first step is to use your OS's package manager to install the \verb+check+ package.
If your OS doesn't have that package, you can download it from \url{http://check.sourceforge.net/},
build it and install it.
\\\\
To help clamav's configure script locate \verb+check+, it is recommended that you install \verb+pkg-config+, preferably
using your OS's package manager, or from \url{http://pkg-config.freedesktop.org}.
\\\\
The recommended way to run unit-tests is the following, which ensures you will get an error if unit tests cannot be built:
\footnote{The configure script in ClamAV automatically enables the unit tests, if it finds the check framework, however it doesn't consider it a fatal error if unit tests cannot be enabled.}
\begin{verbatim}
$ ./configure --enable-check
$ make
$ make check
\end{verbatim}
When \verb+make check+ is finished, you should get a message similar to this:
\begin{verbatim}
==================
All 8 tests passed
==================
\end{verbatim}
If a unit test fails, you get a message similar to the following.
Note that in older versions of make check may report failures due to
the absence of optional packages. Please make sure you have the
latest versions of the components noted in section /ref{sec:components}.
See the next section on how to report a bug when a unit test fails.
\begin{verbatim}
========================================
1 of 8 tests failed
Please report to https://bugzilla.clamav.net/
========================================
\end{verbatim}
If unit tests are disabled (and you didn't use --enable-check), you will get this message:
\begin{verbatim}
*** Unit tests disabled in this build
*** Use ./configure --enable-check to enable them
SKIP: check_clamav
PASS: check_clamd.sh
PASS: check_freshclam.sh
PASS: check_sigtool.sh
PASS: check_clamscan.sh
======================
All 4 tests passed
(1 tests were not run)
======================
\end{verbatim}
Running \verb+./configure --enable-check+ should tell you why.
\subsection{Reporting a unit test failure bug}
If \verb+make check+ says that some tests failed we encourage you to report a bug on our bugzilla: \url{https://bugzilla.clamav.net}.
The information we need is:
\begin{itemize}
\item The exact output from \verb+make check+
\item Output of \verb+uname -mrsp+
\item your \verb+config.log+
\item The following files from the \verb+unit_tests/+ directory:
\begin{itemize}
\item \verb+test.log+
\item \verb+clamscan.log+
\item \verb+clamdscan.log+
\end{itemize}
\item \verb+/tmp/clamd-test.log+ if it exists
\item where and how you installed the check package
\item Output of \verb+pkg-config check --cflags --libs+
\item Optionally if \verb+valgrind+ is available on your platform, the output of the following:
\begin{verbatim}
$ make check
$ CK_FORK=no ./libtool --mode=execute valgrind unit_tests/check_clamav
\end{verbatim}
\end{itemize}
\subsection{Obtain Latest ClamAV anti-virus signature databases}
Before you can run ClamAV in daemon mode (clamd), 'clamdscan',
or 'clamscan' which is ClamAV's command line virus scanner,
you must have ClamAV Virus Database (.cvd) file(s) installed
in the appropriate location on your system. The default
location for these database files are /usr/local/share/clamav
(in Linux/Unix).
\\\\
Here is a listing of currently available ClamAV Virus Database Files:
\begin{itemize}
\item bytecode.cvd (signatures to detect bytecode in files)
\item main.cvd (main ClamAV virus database file)
\item daily.cvd (daily update file for ClamAV virus databases)
\item safebrowsing.cvd (virus signatures for safe browsing)
\end{itemize}
These files can be downloaded via HTTP from the main ClamAV website
or via the 'freshclam' utility on a periodic basis. Using 'freshclam'
is the preferred method of keeping the ClamAV virus database files
up to date without manual intervention (see section \ref{conf:freshclam} for
information on how to configure 'freshclam' for automatic updating and section
\ref{sec:freshclam} for additional details on freshclam).
\section{Configuration}
Before proceeding with the steps below, you should
run the 'clamconf' command, which gives important information
about your ClamAV configuration. See section \ref{sec:clamconf}
for more details.
\subsection{clamd}
Before you start using the daemon you have to edit the configuration file
(in other case \verb+clamd+ won't run):
\begin{verbatim}
$ clamd
ERROR: Please edit the example config file /etc/clamd.conf.
\end{verbatim}
This shows the location of the default configuration file. The format and
options of this file are fully described in the \emph{clamd.conf(5)}
manual. The config file is well commented and configuration should be
straightforward.
\subsubsection{On-access scanning}
One of the interesting features of \verb+clamd+ is on-access scanning
based on fanotify, included in Linux since kernel 2.6.36.
\textbf{This is not required to run clamd}. At the moment the fanotify header is
only available for Linux.
\\\\
Configure on-access scanning in \verb+clamd.conf+ and read the
\ref{On-access} section for on-access scanning usage.
\subsection{clamav-milter}\label{sec:clamavmilter}
ClamAV $\ge0.95$ includes a new, redesigned clamav-milter. The most notable
difference is that the internal mode has been dropped and now a working
clamd companion is required. The second important difference is that now
the milter has got its own configuration and log files.
\\\\
To compile ClamAV with the clamav-milter just run \verb+./configure+
\verb+--enable-milter+ and make as usual. In order to use the
'--enable-milter' option with 'configure', your system MUST have the milter
library installed. If you use the '--enable-milter' option without the
library being installed, you will most likely see output like this during
'configure':
\begin{verbatim}
checking for libiconv_open in -liconv... no
checking for iconv... yes
checking whether in_port_t is defined... yes
checking for in_addr_t definition... yes
checking for mi_stop in -lmilter... no
checking for library containing strlcpy... no
checking for mi_stop in -lmilter... no
configure: error: Cannot find libmilter
\end{verbatim}
At which point the 'configure' script will stop processing.
\\\\
Please consult your MTA's manual on how to connect ClamAV with the milter.
\subsection{Testing}
Try to scan recursively the source directory:
\begin{verbatim}
$ clamscan -r -l scan.txt clamav-x.yz
\end{verbatim}
It should find some test files in the clamav-x.yz/test directory.
The scan result will be saved in the \verb+scan.txt+ log file
\footnote{To get more info on clamscan options run 'man clamscan'}.
To test \verb+clamd+, start it and use \verb+clamdscan+ (or instead connect
directly to its socket and run the SCAN command):
\begin{verbatim}
$ clamdscan -l scan.txt clamav-x.yz
\end{verbatim}
Please note that the scanned files must be accessible by the user running
\verb+clamd+ or you will get an error.
\subsection{Setting up auto-updating}\label{conf:freshclam}
\verb+freshclam+ is the automatic database update tool for Clam AntiVirus.
It can work in two modes:
\begin{itemize}
\item interactive - on demand from command line
\item daemon - silently in the background
\end{itemize}
\verb+freshclam+ is advanced tool: it supports scripted updates (instead
of transferring the whole CVD file at each update it only transfers the
differences between the latest and the current database via a special
script), database version checks through DNS, proxy servers (with
authentication), digital signatures and various error scenarios.
\textbf{Quick test: run freshclam (as superuser) with no parameters
and check the output.} If everything is OK you may create the log file in
/var/log (owned by \emph{clamav} or another user \verb+freshclam+ will be
running as):
\begin{verbatim}
# touch /var/log/freshclam.log
# chmod 600 /var/log/freshclam.log
# chown clamav /var/log/freshclam.log
\end{verbatim}
Now you \emph{should} edit the configuration file \verb+freshclam.conf+
and point the \emph{UpdateLogFile} directive to the log file. Finally, to
run \verb+freshclam+ in the daemon mode, execute:
\begin{verbatim}
# freshclam -d
\end{verbatim}
The other way is to use the \emph{cron} daemon. You have to add the
following line to the crontab of \textbf{root} or \textbf{clamav} user:
{\small
\begin{verbatim}
N * * * * /usr/local/bin/freshclam --quiet
\end{verbatim}}
\noindent to check for a new database every hour. \textbf{N should be a
number between 3 and 57 of your choice. Please don't choose any multiple
of 10, because there are already too many clients using those time slots.}
Proxy settings are only configurable via the configuration file and
\verb+freshclam+ will require strict permission settings for the config
file when \verb+HTTPProxyPassword+ is turned on.
\begin{verbatim}
HTTPProxyServer myproxyserver.com
HTTPProxyPort 1234
HTTPProxyUsername myusername
HTTPProxyPassword mypass
\end{verbatim}
\subsubsection{Closest mirrors}
The \verb+DatabaseMirror+ directive in the config file specifies the
database server \verb+freshclam+ will attempt (up to \verb+MaxAttempts+
times) to download the database from. The default database mirror
is \url{database.clamav.net} but multiple directives are allowed.
In order to download the database from the closest mirror you should
configure \verb+freshclam+ to use \url{db.xx.clamav.net} where xx
represents your country code. For example, if your server is in "Ascension
Island" you should have the following lines included in \verb+freshclam.conf+:
\begin{verbatim}
DNSDatabaseInfo current.cvd.clamav.net
DatabaseMirror db.ac.clamav.net
DatabaseMirror database.clamav.net
\end{verbatim}
The second entry acts as a fallback in case the connection to the first
mirror fails for some reason. The full list of two-letters country codes
is available at \url{http://www.iana.org/cctld/cctld-whois.htm}
\section{Usage}
\subsection{Clam daemon}\label{clamd}
\verb+clamd+ is a multi-threaded daemon that uses \emph{libclamav}
to scan files for viruses. It may work in one or both modes listening on:
\begin{itemize}
\item Unix (local) socket
\item TCP socket
\end{itemize}
The daemon is fully configurable via the \verb+clamd.conf+ file
\footnote{man 5 clamd.conf}. \verb+clamd+ recognizes the following commands:
\begin{itemize}
\item \textbf{PING}\\
Check the daemon's state (should reply with "PONG").
\item \textbf{VERSION}\\
Print program and database versions.
\item \textbf{RELOAD}\\
Reload the databases.
\item \textbf{SHUTDOWN}\\
Perform a clean exit.
\item \textbf{SCAN file/directory}\\
Scan file or directory (recursively) with archive support
enabled (a full path is required).
\item \textbf{RAWSCAN file/directory}\\
Scan file or directory (recursively) with archive and special file
support disabled (a full path is required).
\item \textbf{CONTSCAN file/directory}\\
Scan file or directory (recursively) with archive support
enabled and don't stop the scanning when a virus is found.
\item \textbf{MULTISCAN file/directory}\\
Scan file in a standard way or scan directory (recursively) using
multiple threads (to make the scanning faster on SMP machines).
\item \textbf{ALLMATCHSCAN file/directory}\\
ALLMATCHSCAN works just like SCAN except that it sets a mode
where, after finding a virus within a file, continues scanning for
additional viruses.
\item \textbf{INSTREAM}\\
\emph{It is mandatory to prefix this command with \textbf{n} or
\textbf{z}.}\\
Scan a stream of data. The stream is sent to clamd in chunks,
after INSTREAM, on the same socket on which the command
was sent. This avoids the overhead of establishing new TCP
connections and problems with NAT. The format of the chunk is:
\verb+<length><data>+ where \verb+<length>+ is the size of the
following data in bytes expressed as a 4 byte unsigned integer in
network byte order and \verb+<data>+ is the actual chunk. Streaming
is terminated by sending a zero-length chunk. Note: do not exceed
StreamMaxLength as defined in clamd.conf, otherwise clamd will
reply with \emph{INSTREAM size limit exceeded} and close the
connection.
\item \textbf{FILDES}\\
\emph{It is mandatory to newline terminate this command, or prefix
with \textbf{n} or \textbf{z}. This command only works on UNIX
domain sockets.}\\
Scan a file descriptor. After issuing a FILDES command a subsequent
rfc2292/bsd4.4 style packet (with at least one dummy character) is
sent to clamd carrying the file descriptor to be scanned inside the
ancillary data. Alternatively the file descriptor may be sent in
the same packet, including the extra character.
\item \textbf{STATS}\\
\emph{It is mandatory to newline terminate this command, or prefix
with \textbf{n} or \textbf{z}, it is recommended to only use the
\textbf{z} prefix.}\\
On this command clamd provides statistics about the scan queue,
contents of scan queue, and memory usage. The exact reply format is
subject to changes in future releases.
\item \textbf{IDSESSION, END}\\
\emph{It is mandatory to prefix this command with \textbf{n} or
\textbf{z}, also all commands inside \textbf{IDSESSION} must be
prefixed.}\\
Start/end a clamd session. Within a session multiple
SCAN, INSTREAM, FILDES, VERSION, STATS commands can be sent on the
same socket without opening new connections. Replies from clamd
will be in the form \verb+<id>: <response>+ where \verb+<id>+ is
the request number (in ASCII, starting from 1) and \verb+<response>+
is the usual clamd reply. The reply lines have the same delimiter
as the corresponding command had. Clamd will process the commands
asynchronously, and reply as soon as it has finished processing.
Clamd requires clients to read all the replies it sent, before
sending more commands to prevent send() deadlocks. The recommended
way to implement a client that uses IDSESSION is with non-blocking
sockets, and a select()/poll() loop: whenever send would block,
sleep in select/poll until either you can write more data, or read
more replies. \emph{Note that using non-blocking sockets without
the select/poll loop and alternating recv()/send() doesn't comply
with clamd's requirements.} If clamd detects that a client has
deadlocked, it will close the connection. Note that clamd may
close an IDSESSION connection too if the client doesn't follow the
protocol's requirements.
\item \textbf{STREAM} (deprecated, use \textbf{INSTREAM} instead)\\
Scan stream: clamd will return a new port number you should
connect to and send data to scan.
\end{itemize}
It's recommended to prefix clamd commands with the letter \textbf{z}
(eg. zSCAN) to indicate that the command will be delimited by a NULL
character and that clamd should continue reading command data until a NULL
character is read. The null delimiter assures that the complete command
and its entire argument will be processed as a single command. Alternatively
commands may be prefixed with the letter \textbf{n} (e.g. nSCAN) to use
a newline character as the delimiter. Clamd replies will honour the
requested terminator in turn. If clamd doesn't recognize the command, or
the command doesn't follow the requirements specified below, it will reply
with an error message, and close the connection.
\noindent
Clamd can handle the following signals:
\begin{itemize}
\item \textbf{SIGTERM} - perform a clean exit
\item \textbf{SIGHUP} - reopen the log file
\item \textbf{SIGUSR2} - reload the database
\end{itemize}
Clamd should not be started in the background using the shell operator
\verb+&+ or external tools. Instead, you should run and wait for clamd
to load the database and daemonize itself. After that, clamd is instantly
ready to accept connections and perform file scanning.
\subsection{Clam\textbf{d}scan}
\verb+clamdscan+ is a simple \verb+clamd+ client. In many cases you can
use it as a \verb+clamscan+ replacement however you must remember that:
\begin{itemize}
\item it only depends on \verb+clamd+
\item although it accepts the same command line options as
\verb+clamscan+ most of them are ignored because they must be
enabled directly in \verb+clamd+, i.e. \verb+clamd.conf+
\item in TCP mode scanned files must be accessible for \verb+clamd+,
if you enabled LocalSocket in clamd.conf then clamdscan will
try to workaround this limitation by using FILDES
\end{itemize}
\subsection{On-access Scanning}\label{On-access}
There is a special thread in \verb+clamd+ that performs on-access
scanning under Linux and shares internal virus database
with the daemon. By default, this thread will only notify you when
potential threats are discovered. If you turn on prevention via
\verb+clamd.conf+ then \textbf{you must follow some important rules when
using it:}
\begin{itemize}
\item Always stop the daemon cleanly - using the SHUTDOWN command or
the\\ SIGTERM signal. In other case you can lose access
to protected files until the system is restarted.
\item Never protect the directory your mail-scanner software
uses for attachment unpacking. Access to all infected
files will be automatically blocked and the scanner (including
\verb+clamd+!) will not be able to detect any viruses. In the
result \textbf{all infected mails may be delivered.}
\item Watch your entire filesystem only using the \verb+clamd.conf+
OnAccessMountPath option. While this will disable on-access prevention,
it will avoid potential system lockups caused by fanotify's blocking
functionality.
\item Using the On-Access Scanner to watch a virtual filesystem will result
in undefined behaviour.
\end{itemize}
The default configuration utilizes inotify to recursively keep track of
directories. If you need to protect more than 8192 directories it will
be necessary to change inotify's \verb+max_user_watches+ value.
\\\\
This can be done temporarily with:
\begin{verbatim}
$ sysctl fs.inotify.max_user_watches=<n>
\end{verbatim}
Where \verb+<n>+ is the new maximum desired.
\\\\
To watch your entire filesystem add the following lines to
\verb+clamd.conf+:
\begin{verbatim}
ScanOnAccess yes
OnAccessMountPath /
\end{verbatim}
Similarly, to protect your home directory add the following lines to
\verb+clamd.conf+:
\begin{verbatim}
ScanOnAccess yes
OnAccessIncludePath /home
OnAccessExcludePath /home/user/temp/dir/of/your/mail/scanning/software
OnAccessPrevention yes
\end{verbatim}
For more configuration options, type 'man clamd.conf' or reference the
example clamd.conf.
\subsection{Clamdtop}
\verb+clamdtop+ is a tool to monitor one or multiple instances of clamd. It
has a (color) ncurses interface, that shows the jobs in clamd's queue,
memory usage, and information about the loaded signature database.
You can specify on the command-line to which clamd(s) it should connect
to. By default it will attempt to connect to the local clamd as defined
in clamd.conf.
\\\\
For more detailed help, type 'man clamdtop' or 'clamdtop --help'.
\subsection{Clamscan}
\verb+clamscan+ is ClamAV's command line virus scanner. It can be used to
scan files and/or directories for viruses. In order for clamscan
to work proper, the ClamAV virus database files must be installed on
the system you are using clamscan on.
\\\\
The general usage of clamscan is: clamscan [options] [file/directory/-]
\\\\
For more detailed help, type 'man clamscan' or 'clamscan --help'.
\subsection{ClamBC}
\verb+clambc+ is Clam Anti-Virus' bytecode testing tool. It can be
used to test files which contain bytecode. For more detailed help,
type 'man clambc' or 'clambc --help'.
\subsection{Freshclam}\label{sec:freshclam}
\verb+freshclam+ is ClamAV's virus database update tool and reads it's
configuration from the file 'freshclam.conf' (this may be
overridden by command line options). Freshclam's default behavior is to
attempt to update databases that are paired with downloaded cdiffs.
Potentially corrupted databases are not updated and are automatically
fully replaced after several failed attempts unless otherwise specified.
\\\\
Here is a sample usage including cdiffs:
{\footnotesize
\begin{verbatim}
$ freshclam
ClamAV update process started at Mon Oct 7 08:15:10 2013
main.cld is up to date (version: 55, sigs: 2424225, f-level: 60, builder: neo)
Downloading daily-17945.cdiff [100%]
Downloading daily-17946.cdiff [100%]
Downloading daily-17947.cdiff [100%]
daily.cld updated (version: 17947, sigs: 406951, f-level: 63, builder: neo)
Downloading bytecode-227.cdiff [100%]
Downloading bytecode-228.cdiff [100%]
bytecode.cld updated (version: 228, sigs: 43, f-level: 63, builder: neo)
Database updated (2831219 signatures) from database.clamav.net (IP: 64.6.100.177)
\end{verbatim}
}
For more detailed help, type 'man clamscan' or 'clamscan --help'.
\subsection{Clamconf}\label{sec:clamconf}
\verb+clamconf+ is the Clam Anti-Virus configuration utility. It is used
for displaying values of configurations options in ClamAV, which
will show the contents of clamd.conf (or tell you if it is not
properly configured), the contents of freshclam.conf, and display
information about software settings, database, platform, and build
information. Here is a sample clamconf output:
{\footnotesize
\begin{verbatim}
$ clamconf
Checking configuration files in /etc/clamav
Config file: clamd.conf
-----------------------
ERROR: Please edit the example config file /etc/clamav/clamd.conf
Config file: freshclam.conf
---------------------------
ERROR: Please edit the example config file /etc/clamav/freshclam.conf
clamav-milter.conf not found
Software settings
-----------------
Version: 0.98.2
Optional features supported: MEMPOOL IPv6 AUTOIT_EA06 BZIP2 RAR JIT
Database information
--------------------
Database directory: /xclam/gcc/release/share/clamav
WARNING: freshclam.conf and clamd.conf point to different database directories
print_dbs: Can't open directory /xclam/gcc/release/share/clamav
Platform information
--------------------
uname: Linux 3.5.0-44-generic #67~precise1-Ubuntu SMP Wed Nov 13 16:20:03 UTC 2013 i686
OS: linux-gnu, ARCH: i386, CPU: i686
Full OS version: Ubuntu 12.04.3 LTS
zlib version: 1.2.3.4 (1.2.3.4), compile flags: 55
Triple: i386-pc-linux-gnu
CPU: i686, Little-endian
platform id: 0x0a114d4d0404060401040604
Build information
-----------------
GNU C: 4.6.4 (4.6.4)
GNU C++: 4.6.4 (4.6.4)
CPPFLAGS:
CFLAGS: -g -O0 -D_LARGEFILE_SOURCE -D_LARGEFILE64_SOURCE
CXXFLAGS:
LDFLAGS:
Configure: '--prefix=/xclam/gcc/release/' '--disable-clamav' '--enable-debug' 'CFLAGS=-g -O0'
sizeof(void*) = 4
Engine flevel: 77, dconf: 77
\end{verbatim}
}
For more detailed help, type 'man clamconf' or 'clamconf --help'.
\subsection{Output format}
\subsubsection{clamscan}
\verb+clamscan+ writes all regular program messages to \textbf{stdout} and
errors/warnings to \textbf{stderr}. You can use the option \verb+--stdout+
to redirect all program messages to \textbf{stdout}. Warnings and error
messages from \verb+libclamav+ are always printed to \textbf{stderr}.
A typical output from \verb+clamscan+ looks like this:
\begin{verbatim}
/tmp/test/removal-tool.exe: Worm.Sober FOUND
/tmp/test/md5.o: OK
/tmp/test/blob.c: OK
/tmp/test/message.c: OK
/tmp/test/error.hta: VBS.Inor.D FOUND
\end{verbatim}
When a virus is found its name is printed between the \verb+filename:+ and
\verb+FOUND+ strings. In case of archives the scanner depends on libclamav
and only prints the first virus found within an archive:
\begin{verbatim}
$ clamscan malware.zip
malware.zip: Worm.Mydoom.U FOUND
\end{verbatim}
When using the --allmatch(-z) flag, clamscan may print multiple virus
\verb+FOUND+ lines for archives and files.
\subsubsection{clamd}
The output format of \verb+clamd+ is very similar to \verb+clamscan+.
\begin{verbatim}
$ telnet localhost 3310
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
SCAN /home/zolw/test
/home/zolw/test/clam.exe: ClamAV-Test-File FOUND
Connection closed by foreign host.
\end{verbatim}
In the \textbf{SCAN} mode it closes the connection when the first virus
is found.
\begin{verbatim}
SCAN /home/zolw/test/clam.zip
/home/zolw/test/clam.zip: ClamAV-Test-File FOUND
\end{verbatim}
\textbf{CONTSCAN} and \textbf{MULTISCAN} don't stop scanning in case
a virus is found.\\
Error messages are printed in the following format:
\begin{verbatim}
SCAN /no/such/file
/no/such/file: Can't stat() the file. ERROR
\end{verbatim}
\section{LibClamAV}
Libclamav provides an easy and effective way to add a virus protection into
your software. The library is thread-safe and transparently recognizes and
scans within archives, mail files, MS Office document files, executables
and other special formats.
\subsection{License}
Libclamav is licensed under the GNU GPL v2 license. This means you are
\textbf{not allowed} to link commercial, closed-source software
against it. All software using libclamav must be GPL compliant.
\subsection{Supported formats and features}
\subsubsection{Executables}
The library has a built-in support for 32- and 64-bit Portable Executable,
ELF and Mach-O files. Additionally, it can handle PE files compressed or
obfuscated with the following tools:
\begin{itemize}
\item Aspack (2.12)
\item UPX (all versions)
\item FSG (1.3, 1.31, 1.33, 2.0)
\item Petite (2.x)
\item PeSpin (1.1)
\item NsPack
\item wwpack32 (1.20)
\item MEW
\item Upack
\item Y0da Cryptor (1.3)
\end{itemize}
\subsubsection{Mail files}
Libclamav can handle almost every mail file format including TNEF
(winmail.dat) attachments.
\subsubsection{Archives and compressed files}
The following archive and compression formats are supported by internal
handlers:
\begin{itemize}
\item Zip (+ SFX)
\item RAR (+ SFX)
\item 7Zip
\item Tar
\item CPIO
\item Gzip
\item Bzip2
\item DMG
\item IMG
\item ISO 9660
\item PKG
\item HFS+ partition
\item HFSX partition
\item APM disk image
\item GPT disk image
\item MBR disk image
\item XAR
\item XZ
\item MS OLE2
\item MS Cabinet Files (+ SFX)
\item MS CHM (Compiled HTML)
\item MS SZDD compression format
\item BinHex
\item SIS (SymbianOS packages)
\item AutoIt
\item NSIS
\item InstallShield
\end{itemize}
\subsubsection{Documents}
The most popular file formats are supported:
\begin{itemize}
\item MS Office and MacOffice files
\item RTF
\item PDF
\item HTML
\end{itemize}
In the case of Office, RTF and PDF files, libclamav will only extract the
embedded objects and will not decode the text data itself. The text
decoding and normalization is only performed for HTML files.
\subsubsection{Data Loss Prevention}
Libclamav includes a DLP module which can detect the following
credit card issuers: AMEX, VISA, MasterCard, Discover, Diner's Club,
and JCB and U.S. social security numbers inside text files.
\\\\
Future versions of Libclamav may include additional features to
detect other credit cards and other forms of PII (Personally
Identifiable Information) which may be transmitted without the
benefit of being encrypted.
\subsubsection{Others}
Libclamav can handle various obfuscators, encoders, files vulnerable to
security risks such as:
\begin{itemize}
\item JPEG (exploit detection)
\item RIFF (exploit detection)
\item uuencode
\item ScrEnc obfuscation
\item CryptFF
\end{itemize}
\subsection{API}
\subsubsection{Header file}
Every program using libclamav must include the header file \verb+clamav.h+:
\begin{verbatim}
#include <clamav.h>
\end{verbatim}
\subsubsection{Initialization}
Before using libclamav, you should call \verb+cl_init()+ to initialize
it. \verb+CL_INIT_DEFAULT+ is a macro that can be passed to \verb+cl_init()+
representing the default initialization settings. When it's done, you're ready
to create a new scan engine by calling \verb+cl_engine_new()+. To free resources
allocated by the engine use \verb+cl_engine_free()+. Function prototypes:
\begin{verbatim}
int cl_init(unsigned int options);
struct cl_engine *cl_engine_new(void);
int cl_engine_free(struct cl_engine *engine);
\end{verbatim}
\verb+cl_init()+ and \verb+cl_engine_free()+ return \verb+CL_SUCCESS+
on success or another code on error. \verb+cl_engine_new()+ return
a pointer or NULL if there's not enough memory to allocate a new
engine structure.
\subsubsection{Database loading}
The following set of functions provides an interface for loading
the virus database:
\begin{verbatim}
const char *cl_retdbdir(void);
int cl_load(const char *path, struct cl_engine *engine,
unsigned int *signo, unsigned int options);
\end{verbatim}
\verb+cl_retdbdir()+ returns the default (hardcoded) path to the directory
with ClamAV databases.
\verb+cl_load()+ loads a single database file or all databases from a
given directory (when \verb+path+ points to a directory). The second
argument is used for passing in the pointer to the engine that should
be previously allocated with \verb+cl_engine_new()+. A number of loaded
signatures will be \textbf{added} to \verb+signo+ \footnote{Remember to
initialize the virus counter variable with 0.}. The last argument can
pass the following flags:
\begin{itemize}
\item \textbf{CL\_DB\_STDOPT}\\
This is an alias for a recommended set of scan options.
\item \textbf{CL\_DB\_PHISHING}\\
Load phishing signatures.
\item \textbf{CL\_DB\_PHISHING\_URLS}\\
Initialize the phishing detection module and load .wdb and .pdb files.
\item \textbf{CL\_DB\_PUA}\\
Load signatures for Potentially Unwanted Applications.
\item \textbf{CL\_DB\_OFFICIAL\_ONLY}\\
Only load official signatures from digitally signed databases.
\item \textbf{CL\_DB\_BYTECODE}\\
Load bytecode.
\end{itemize}
\verb+cl_load()+ returns \verb+CL_SUCCESS+ on success and another code on
failure.
\begin{verbatim}
...
struct cl_engine *engine;
unsigned int sigs = 0;
int ret;
if((ret = cl_init(CL_INIT_DEFAULT)) != CL_SUCCESS) {
printf("cl_init() error: %s\n", cl_strerror(ret));
return 1;
}
if(!(engine = cl_engine_new())) {
printf("Can't create new engine\n");
return 1;
}
ret = cl_load(cl_retdbdir(), engine, &sigs, CL_DB_STDOPT);
\end{verbatim}
\subsubsection{Error handling}
Use \verb+cl_strerror()+ to convert error codes into human readable
messages. The function returns a statically allocated string:
\begin{verbatim}
if(ret != CL_SUCCESS) {
printf("cl_load() error: %s\n", cl_strerror(ret));
cl_engine_free(engine);
return 1;
}
\end{verbatim}
\subsubsection{Engine structure}
When all required databases are loaded you should prepare the detection
engine by calling \verb+cl_engine_compile()+. In case of failure you
should still free the memory allocated to the engine with
\verb+cl_engine_free()+:
\begin{verbatim}
int cl_engine_compile(struct cl_engine *engine);
\end{verbatim}
In our example:
\begin{verbatim}
if((ret = cl_engine_compile(engine)) != CL_SUCCESS) {
printf("cl_engine_compile() error: %s\n", cl_strerror(ret));
cl_engine_free(engine);
return 1;
}
\end{verbatim}
\subsubsection{Limits}
When you create a new engine with \verb+cl_engine_new()+, it will have
all internal settings set to default values as recommended by the
ClamAV authors. It's possible to check and modify the values (numerical
and strings) using the following set of functions:
\begin{verbatim}
int cl_engine_set_num(struct cl_engine *engine,
enum cl_engine_field field, long long num);
long long cl_engine_get_num(const struct cl_engine *engine,
enum cl_engine_field field, int *err);
int cl_engine_set_str(struct cl_engine *engine,
enum cl_engine_field field, const char *str);
const char *cl_engine_get_str(const struct cl_engine *engine,
enum cl_engine_field field, int *err);
\end{verbatim}
Please don't modify the default values unless you know what you're doing.
Refer to the ClamAV sources (clamscan, clamd) for examples.
\subsubsection{Database checks}
It's very important to keep the internal instance of the database up to
date. You can watch database changes with the \verb+cl_stat..()+ family
of functions.
\begin{verbatim}
int cl_statinidir(const char *dirname, struct cl_stat *dbstat);
int cl_statchkdir(const struct cl_stat *dbstat);
int cl_statfree(struct cl_stat *dbstat);
\end{verbatim}
Initialization:
\begin{verbatim}
...
struct cl_stat dbstat;
memset(&dbstat, 0, sizeof(struct cl_stat));
cl_statinidir(dbdir, &dbstat);
\end{verbatim}
To check for a change you just need to call \verb+cl_statchkdir+ and check
its return value (0 - no change, 1 - some change occurred). Remember to reset
the \verb+cl_stat+ structure after reloading the database.
\begin{verbatim}
if(cl_statchkdir(&dbstat) == 1) {
reload_database...;
cl_statfree(&dbstat);
cl_statinidir(cl_retdbdir(), &dbstat);
}
\end{verbatim}
Libclamav $\ge0.96$ includes and additional call to check the number of
signatures that can be loaded from a given directory:
\begin{verbatim}
int cl_countsigs(const char *path, unsigned int countoptions,
unsigned int *sigs);
\end{verbatim}
The first argument points to the database directory, the second one
specifies what signatures should be counted:
\verb+CL_COUNTSIGS_OFFICIAL+ (official signatures),\\
\verb+CL_COUNTSIGS_UNOFFICIAL+ (third party signatures),
\verb+CL_COUNTSIGS_ALL+ (all signatures). The last argument points
to the counter to which the number of detected signatures will
be added (therefore the counter should be initially set to 0).
The call returns \verb+CL_SUCCESS+ or an error code.
\subsubsection{Data scan functions}
It's possible to scan a file or descriptor using:
\begin{verbatim}
int cl_scanfile(const char *filename, const char **virname,
unsigned long int *scanned, const struct cl_engine *engine,
unsigned int options);
int cl_scandesc(int desc, const char **virname, unsigned
long int *scanned, const struct cl_engine *engine,
unsigned int options);
\end{verbatim}
Both functions will store a virus name under the pointer \verb+virname+,
the virus name is part of the engine structure and must not be released
directly. If the third argument (\verb+scanned+) is not NULL, the
functions will increase its value with the size of scanned data (in
\verb+CL_COUNT_PRECISION+ units).
The last argument (\verb+options+) specified the scan options and supports
the following flags (which can be combined using bit operators):
\begin{itemize}
\item \textbf{CL\_SCAN\_STDOPT}\\
This is an alias for a recommended set of scan options. You
should use it to make your software ready for new features
in the future versions of libclamav.
\item \textbf{CL\_SCAN\_RAW}\\
Use it alone if you want to disable support for special files.
\item \textbf{CL\_SCAN\_ARCHIVE}\\
This flag enables transparent scanning of various archive formats.
\item \textbf{CL\_SCAN\_BLOCKENCRYPTED}\\
With this flag the library will mark encrypted archives as viruses
(Encrypted.Zip, Encrypted.RAR).
\item \textbf{CL\_SCAN\_MAIL}\\
Enable support for mail files.
\item \textbf{CL\_SCAN\_OLE2}\\
Enables support for OLE2 containers (used by MS Office and .msi
files).
\item \textbf{CL\_SCAN\_PDF}\\
Enables scanning within PDF files.
\item \textbf{CL\_SCAN\_SWF}\\
Enables scanning within SWF files, notably compressed SWF.
\item \textbf{CL\_SCAN\_PE}\\
This flag enables deep scanning of Portable Executable files and
allows libclamav to unpack executables compressed with run-time
unpackers.
\item \textbf{CL\_SCAN\_ELF}\\
Enable support for ELF files.
\item \textbf{CL\_SCAN\_BLOCKBROKEN}\\
libclamav will try to detect broken executables and mark them as
Broken.Executable.
\item \textbf{CL\_SCAN\_HTML}\\
This flag enables HTML normalisation (including ScrEnc
decryption).
\item \textbf{CL\_SCAN\_ALGORITHMIC}\\
Enable algorithmic detection of viruses.
\item \textbf{CL\_SCAN\_PHISHING\_BLOCKSSL}\\
Phishing module: always block SSL mismatches in URLs.
\item \textbf{CL\_SCAN\_PHISHING\_BLOCKCLOAK}\\
Phishing module: always block cloaked URLs.
\item \textbf{CL\_SCAN\_STRUCTURED}\\
Enable the DLP module which scans for credit card and SSN
numbers.
\item \textbf{CL\_SCAN\_STRUCTURED\_SSN\_NORMAL}\\
Search for SSNs formatted as xx-yy-zzzz.
\item \textbf{CL\_SCAN\_STRUCTURED\_SSN\_STRIPPED}\\
Search for SSNs formatted as xxyyzzzz.
\item \textbf{CL\_SCAN\_PARTIAL\_MESSAGE}\\
Scan RFC1341 messages split over many emails. You will need to
periodically clean up \verb+$TemporaryDirectory/clamav-partial+
directory.
\item \textbf{CL\_SCAN\_HEURISTIC\_PRECEDENCE}\\
Allow heuristic match to take precedence. When enabled, if
a heuristic scan (such as phishingScan) detects a possible
virus/phish it will stop scan immediately. Recommended, saves CPU
scan-time. When disabled, virus/phish detected by heuristic scans
will be reported only at the end of a scan. If an archive
contains both a heuristically detected virus/phishing, and a real
malware, the real malware will be reported.
\item \textbf{CL\_SCAN\_BLOCKMACROS}\\
OLE2 containers, which contain VBA macros will be marked infected
(Heuristics.OLE2.ContainsMacros).
\end{itemize}
All functions return \verb+CL_CLEAN+ when the file seems clean,
\verb+CL_VIRUS+ when a virus is detected and another value on failure.
\begin{verbatim}
...
const char *virname;
if((ret = cl_scanfile("/tmp/test.exe", &virname, NULL, engine,
CL_SCAN_STDOPT)) == CL_VIRUS) {
printf("Virus detected: %s\n", virname);
} else {
printf("No virus detected.\n");
if(ret != CL_CLEAN)
printf("Error: %s\n", cl_strerror(ret));
}
\end{verbatim}
\subsubsection{Memory}
Because the engine structure occupies a few megabytes of system memory, you
should release it with \verb+cl_engine_free()+ if you no longer need to
scan files.
\subsubsection{Forking daemons}
If you're using libclamav with a forking daemon you should call
\verb+srand()+ inside a forked child before making any calls to the
libclamav functions. This will avoid possible collisions with temporary
filenames created by other processes of the daemon. This procedure
is not required for multi-threaded daemons.
\subsubsection{clamav-config}
Use \verb+clamav-config+ to check compilation information for libclamav.
\begin{verbatim}
$ clamav-config --libs
-L/usr/local/lib -lz -lbz2 -lgmp -lpthread
$ clamav-config --cflags
-I/usr/local/include -g -O2
\end{verbatim}
\subsubsection{Example}
You will find an example scanner application in the clamav source
package (/example). Provided you have ClamAV already installed, execute
the following to compile it:
\begin{verbatim}
gcc -Wall ex1.c -o ex1 -lclamav
\end{verbatim}
\subsection{CVD format}
CVD (ClamAV Virus Database) is a digitally signed tarball containing
one or more databases. The header is a 512-bytes long string with colon
separated fields:
\begin{verbatim}
ClamAV-VDB:build time:version:number of signatures:functionality
level required:MD5 checksum:digital signature:builder name:build time (sec)
\end{verbatim}
\verb+sigtool --info+ displays detailed information on CVD files:
\begin{verbatim}
$ sigtool -i daily.cvd
File: daily.cvd
Build time: 10 Mar 2008 10:45 +0000
Version: 6191
Signatures: 59084
Functionality level: 26
Builder: ccordes
MD5: 6e6e29dae36b4b7315932c921e568330
Digital signature: zz9irc9irupR3z7yX6J+OR6XdFPUat4HIM9ERn3kAcOWpcMFxq
Fs4toG5WJsHda0Jj92IUusZ7wAgYjpai1Nr+jFfXHsJxv0dBkS5/XWMntj0T1ctNgqmiF
+RLU6V0VeTl4Oej3Aya0cVpd9K4XXevEO2eTTvzWNCAq0ZzWNdjc
Verification OK.
\end{verbatim}
\subsection{Graphics}
The current ClamAV logo was created by Alicia Willet, Talos.
\subsection{OpenAntiVirus}
Our database includes the virus database (about 7000 signatures) from
OpenAntiVirus (\url{http://OpenAntiVirus.org}).
\end{document}