I dont really buy that whole... there are too few mac users for people to create viruses for them...
If Mac users and the commercials are constantly bragging about how its hard to get a virus on their Mac, there would be a ton of virus programmers trying to prove them wrong.
And they have, there are some viruses/trojans/worms that are capable of infecting OS X. But not nearly as many as there are for Windows. OSX is simply a more idiot proof OS.
Best way to prevent viruses? Don't surf for porn
No, i am not a mac user and nor will I ever be. Their designs are a bit too form over function for me.. too trendy, plus I like to game on my PC.