[ADd]

You'd be amazed how many linux system are compromised, a search through the web for server logs will show how many zombies there are out there. Some of these are Linux servers, which have been compromised and are being used to store attack scripts.

The best defence is the user themselves, and their knowledge of a system. Any system can be compromised, and information stolen - from the simple user to a bank or corporation.

AVG and avast are both very good, as is Kaspersky, and anti-vir - go for the one that suits you best - but back it up with online scans from tme to time, and anti-spyware progs