Hi Folks,
SO there’s an actual trojan out there that affect Mac computers – how bout that?
It’s not a virus, as it can’t propagate itself, but it’s annoying just the same.
What happens is this:
You see a pop up on your screen (that came from a compromised website you visited) that tells you you’re infected with a virus, and to download this program to fix it. DON’T DO THIS.
If you do download, and then install it (it will ask you for your Mac password), it will then inform you that you are infected with a bajillion viruses and the only way to clean them is to register and pay for the software. DON’T DO THIS.
So really, if you exercise caution (and hey, your mac doesn’t HAVE virus protection, does it, so how does this thing know) you really don’t have anything to fear.
A good rule of thumb, whether a Mac or a PC, is to not download or install ANY program that you don’t know.

If you have gone and infected yourself (two of my clients have to date), it’s pretty simple to get rid of.
Open Activity Monitor via search, or in Applications, Utilities.
Find any Mac Defender or Mac Protector like thing in the processes list, and click the big red Quit Process button. Yes it’s OK.
Once you’ve done this, go to your Applications folder, and find and trash the Mac Defender / Mac Protector application in there, and then for good measure, empty the trash. A system reboot wouldn’t hurt, but wouldn’t be necessary.

And no, I haven’t changed my mind about virus protection on the mac – still think it’s a waste of money at this point.