Tripwire is a good product but it's not a antivirus solution.

*nix has seldom virus but as popularity rises more and more threats will be discovered and a good antivirus solution is always a good and wise choice.

What is tripwire?

Tripwire is a tool that checks to see what has changed on your system. The program monitors key attributes of files that should not change, including binary signature, size, expected change of size, etc. The hard part is doing it the right way, balancing security, maintanence, and functionality.

Source: http://www.tripwire.org/qanda/faq.php