ClamAV is probably your best bet. That said, the question is, what do you scan? It can be used several ways, typically scanning files on demand... its not an intrusion detection system like most MS Windows scanners, where it automatically scans every file being read or written (while slowing the system down 300%). If your system isn't handling 'files', it becomes harder to figure out what to do with it... I suppose you could crontab a nightly scan of all files on the system with clamscan, or something. of course, you want to run freshclam once or twice a day to pick up new definitions. I most typically use ClamAV in my email flow, where MailScanner runs every inbound (and outbound) email through it. I've also run it periodically against file systems used as a file server.