Originally Posted by HILife
That is a major misconception. Macs can get malware just like any other computer in the world. There are just less of them in the world because of Mac's smaller market share. Why write a program to infect macs that have maybe 10% market share, when you can write a +80% market share windows.
With all that said, go Linux, because it's free and because you like doing stuff the hard way.
Let me echo HiLife. If you get plugged into the vulnerability community, you will find plenty of issue with BSD / Mac.
Virus scanners are dead by the way. Most companies have moved to threat prevention and heuristic scanning to prevent the pattern of attacks. Virus scan engines are retroactive.