Clam Anti-Virus is a GPL'd virus scanner implemented in C, which uses the OpenAntiVirus pattern database. It has daemon/command-line modes of operation and built-in patterns update tools. http://clamav.elektrapro.com/ The category app-admin seems appropriate.
Created attachment 7655 [details] Ebuild script
net-mail/clamav version 0.54 is now in portage.