From new's:

A Survey released by Evans Data reveals that 92% of respondents have never had their Linux systems infected with a virus.

The survey, titled Summer 2004 Linux Development Survey, also reports that 78% of Linux developers have never had their systems hacked.

Additionally, a mere seven per cent had been hacked three or more times.

According to the survey, of the 22% hacked users, 23% of intrusions were made by users with working, legit login ID's.
Gotta love the *nix security Official Link to Article