Originally Posted by Kaefer

None. I have not had one in years, and I've had no problems at all. Not ONE virus, not ONE trojan horse... nothing. You see, to install anything on OSX, you (the user -- the owner or administrator of the machine) must actually approve it (enter password and allow it to install). Twice. Windows allows anyone to install anything on your machine in the background without your knowledge, which is why it's so suceptible to viruses. Not so with the Mac. Go ahead and buy an anti-virus application if it makes you feel better... but you won't need it.

Juan