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.

Here is a list of the main features:
  * command-line scanner
  * fast, multi-threaded daemon with support for on-access scanning
  * milter interface for sendmail
  * advanced database updater with support for scripted updates and digital 
    signatures
  * virus scanner C library
  * on-access scanning (Linux and FreeBSD)
  * virus database updated multiple times per day (see home page for total 
    number of signatures)
  * built-in support for various archive formats, including Zip, RAR, Tar, 
    Gzip, Bzip2, OLE2, Cabinet, CHM, BinHex, SIS and others
  * built-in support for almost all mail file formats
  * built-in support for ELF executables and Portable Executable files 
    compressed with UPX, FSG, Petite, NsPack, wwpack32, MEW, Upack and 
    obfuscated with SUE, Y0da Cryptor and others
  * built-in support for popular document formats including MS Office and 
    MacOffice files, HTML, RTF and PDF