Sounds very similar to what I had happen last week. I don't now what the site was, but I did notice that the box appeared to be scanning what were Windows system files, so it couldn't have been real. I didn't download anything and I would think that if you didn't then you are probably safe. I am far from an expert on this though and am sure that someone with more expertise will reply also. I have learned that the best thing to do is to empty cache, cookies and delete history and shut down the browser. Don't even try to close the box I have read. I don't remember if I did that or not. I think there are some nasty things going around right now trying to fool us into installing them on our Macs. I agree it is a very scary exerience. I was shaking when it first happened to me.

Thanks so much. i feel better that others have had the problem. I did not try to shut it down and did not download anything so I hope I am ok.

If you're running under Windows, I suggest you download and install Microsoft's Security Essentials. It protects against these types of attacks and tends to find stuff that other anti-virus scanners don't find. You're system could be infected because of that bogus, evil anti-virus scan. Install and run the software while in safe mode.