This weekend I was browsing on the web and after doing so, found that my browser had been hijacked. I'd not clicked on anything (I SWEAR!) ;-) Needless to say, I went about the usual methods of determining what the problem was and how to fix it. Hijackthis noted a dll connected to the browser as well as launching as a BHO. The hijacking manifested as html doc on my system which was being called by the dll. Instead of launching my Internet homepage, it would launch the local file which was a search engine type page. This would then launch a pop-up ad which stated "your system is infected with a pop-up... download (name) pop-up stopper."
After deleting the offending entries in hijackthis, I opened the browser and found the hijacker re-established itself. Tried spybot, but it didn't find the problem
Finally, installed Ad-Aware and killed it. Had to do it again after I rebooted...
Watch those sites folks.