Linux may be more resilient against viruses, but there are still good reasons to install some form of antivirus software. Not only does it protect the computer against future threats, it also makes sure that viruses are not passed on to Windows users.
You can read our full review of AVG free for Linux here.
The download here is for Suse Linux. There are alternative versions for Red Hat and Mandriva also available.
The familiar interface of AVG is maintained from the Windows version, making this ideal for Linux newcomers.
There are some detailed system requirements, most of which should be met by the distributions listed above. More information can be found in the AVG free for Linux manual. This is in PDF format, so you will need the Adobe Reader.