Sorry, it was months back and I do not have a link. You can Google it though
You must remember when there were one or two viruses out there for OSX about 4 or so months ago, one that supposedly did not need you to enter your root password to install. It was posted on many places on the web. Apple sent a SU to protect OSX against it, however, it was pretty far after the fact.
Ahhhh.....I just saw the "snipe hunt" link. The viruses I am talking about were talked about on most mainstream security forums. I do believe that they were true threats. Enough for Apple to update OSX to protect against them.
As Brian has already stated, that was NOT a virus. While technically speaking, there are variants of viruses out there in general (trojan can be one), that was simply a pop up in the form of adware/malware. The term malware is broad in scope and in this case represented "adware". Those using Safari who had the "open safe downloads" box checked, were easiest to get to, while those of us using other browsers had to physically look in the downloads folder and then physically click on the download, then give admin privileges in order to run the more or less benign code.
They also had a variant that would download if you clicked on a particular image in Google's image database. But essentially, it was just a very rudimentary attempt to try and get credit card info from naive switchers.
But a self propagating, typical kind of virus it was NOT. Not by a long shot. I think it's important to understand the different types of "viruses" out there, and how they are spread and how they behave. Because once one understands those things, the easier it would be to understand why your average AV software is unnecessary for OS X.
I only ever ran AVG for Windows, and was just fine with that. I did of course run spybot, and other malware checkers, but that's because those sorts of things are a different animal. Surf safely, don't download from unknown sources, don't visit questionable sites and don't click on everything that says click me! Having a good firewall/router is more than enough after all of that. This is years of experience talking here, nothing more.
Doug