There's a ridiculous rumor running around the net that Linux is so inherently secure -- or so securely obscure -- that you shouldn't even bother running an antivirus on it. But frankly, that's just not true. While it is true that there are very few significant viruses that target Linux today, the plain fact is that these threats do exist, and they're far more likely to infect an unprotected PC than one that's running an antivirus app. The idea of foregoing antivirus protection just because there are relatively few extant threats is akin to driving with your eyes closed because traffic is fairly light. Either way, you're asking for trouble. Fortunately, there are two great AV options made explicitly for Linux home users, and they're both available for free.
F-Prot - www.f-prot.com
FRISK's F-Prot antivirus is free to home users, complete with online definition updates. Unlike ClamAV and many other Linux antivirus apps, F-Prot is made specifically for workstations, rather than for mail servers. So it won't waste your time searching for virus threats that are irrelevant to you. It will, however, detect macro viruses that may infect office documents, so you can safely share files with your Windows-based compatriots without helping them spread their own infections.
F-Prot is CLI-based, so you execute it with a variety of command switches, such as "f-prot -disinf -report=/home/<username>/fprotreport". The lack of a CLI makes f-prot fast and efficient, but may pose problems for newbs who aren't familiar with cron jobs. But if you're OK with cron, it takes mere minutes to set up automatic updates and regular scans with f-prot.
AVG - free.grisoft.com
Dedicated Max PC readers are no strangers to the virtues of AVG Antivirus, but you may not realize that Grisoft also offers a free version of AVG for Linux workstations. Like F-Prot, AVG works great from the command line, but it also includes a friendly GUI for those who are accustomed to Windows (or who just want to click buttons rather than type).
AVG is available in four different packages, for Debian, Red Hat, SUSE, and Mandriva, so be sure to pick the one that matches your distro to avoid undue hassles. In my tests with Ubuntu, I had to modify some settings* to get updates and scanning to work correctly from the GUI. (Although it worked fine right off the bat using sudo at the command line.) But even for a relative newb, it should be pretty painless.
Every time I mention a few good Linux options, I invariably leave out others, and this post is no exception. There are lots of good antivirus utilities out there for Linux, but these two are among the simplest and most effective for desktop users, and they're free. If you'd like to mention others I left out, please chime in with a comment below. But whatever you do, please don't keep spreading the unhelpful rumor that Linux is virus-free.
*For AVG users running Ubuntu Feisty, here's how to get updates and scanning to work correctly from the GUI.
1. In System > Preferences > Main Menu, select Accessories and then right-click AVG for Linux Workstation. Choose Properties, and then add gksudo to the front of the command entry, so it should read "gksudo avggui". This will launch the program as administrator, which will let Update run with the proper permissions.
2. In System > Administration > Users and Groups, select Manage Groups, then scroll down the list until you see avg. Highlight it, then click Properties. Put a checkmark next to each of the entries in this menu, which should be root, your username, and avg. Click OK and close out the Users and Groups menus. Now you'll be able to run scans without erroring out after 5 seconds.