Apokalipse is correct. The only virus that caused the most damage to Macs, was a Microsoft issued virus in the mid nineties. All current Macs are now immune to this virus and many many more. I had loaded a virus last year from a CD-Rom i got in some cereal. The virus was intended to work on the Mac OS, but it didn't. It did however replicate itself so many times that it got annoying, but a quick run of Disk First Aide, and it was gone for good. I've never had to worry about getting a virus on my Mac. That's one of the MAIN reasons why I bought it. No trouble shooting.
Nobody really wants something that they're always having to fix.