"You probably know that viruses pose no immediate danger to
Linux, but maybe you want to protect some Windows machines attached
to your Linux mail server. I compared a commercial product, Frisk
Software's F-Prot, and a free open source product, ClamAV, both
running on a Linux server.
"F-Prot consists of three packages for Linux: Antivirus for File
Servers, Mail Servers, and Workstations. Each is priced
individually, but you get a discount for multiple users. You can
download them all free for a 30-day trial period. They support the
main Linux distributions, and installation is simple..."