So after this morning's earthquake in Chile, it appears that the lovely new (and effective) fake anti-virus software is being propagated out through bad web sites that have cloaked themselves as being about the earthquake and had gotten themselves to the top of the search results on engines like Google. Unwary clickers would go to their site and voila, you've got a virus and they'd LOOOVE to fix it for you. Sigh. Sure, the bad sites will start going further down the list as the day wears on and real sites start getting back to the top based on volume and people linking to those articles.
"Whew!" you say, "Better that this isn't something that is on MY site! Man I could get in trouble for that!" Well, other than just plain old bad sites willingly hosting the fake anti-virus software, you have to be aware that there are other valid sites that the software is coming from (until it is noticed and removed). Is it one of yours?
If you have XSS allowed on your site, especially if you are hosting a forum or discussion group at all, you may have links right to that software ON YOUR SITE. You have to make sure you have XSS covered in all places. If I am a hacker, I'd set up the bad site for search results to have an IFRAME that points to your site which has another hidden IFRAME that grabs the software from a third server. You may be an unwitting contributor to today's malware distribution.
Lock it up and keep your sites out of the mix!