ClamAV

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. It has built-in support for all standard mail file formats, various archive formats, executable formats, and popular document formats. The core of the package is an anti-virus engine available in a form of shared library.

Talos authors all detection for ClamAV.

IRC:

Service: irc.freenode.net
Channel: #clamav