A few weeks back I commented on the dearth of viruses infecting Apple OS X, but I now stand corrected.
It is pretty easy to infect a Mac after all.
Just install anti-virus software, and make sure the DAT files are up to date!
Symantec screwed up, sending out what they called “a rogue update,” that caused all kinds of problems for Mac users. Read the article in the above link for more information on what Symantec Anti-Virus for Mac versions were affected.