Not wishing to start a Mac/PC war, but to say you are safe using a Mac is horsiepoo.
As I know after spending several hours clearing out an infection on someone else's machine which was transmitted via MSN. If Mac OS was so safe, they wouldn't be patching security holes, would they.....
If you don't believe me when I say you are NOT secure just because you use a Mac, lookee here :-
http://www.securemac.com/