I just got what appeared to be a windows malware warning while I was on the main page of an FFXI forum. It made me suspicious because it said "User at IP address blah blah has gained control of your computer and has accessed your credit card information." It also said that I did not have all my Windows Security stuff activated, when I know for a fact that our work PCs are locked up tighter than Fort Knox. (Hell, all cookies are frickin deleted every time we boot up!)
I suspect I rolled over an ad which is masquerading as an offical Windows security warning. I don't mind pop ups, but this particular ad took me away from the Alla page I was on and jumped me over to an entirely different website so that I had to hit the back button. (I'll admit, it gave me the jumps too before I realized that it made NO SENSE.)
If it happens again I'll try to grab a screenshot.