I seem to be afflicted by a trojan/virus. It comes up in Spybot as win32.downloader.gen, and Spybot cannot remove. I am using Norton Internet Security 184.108.40.206 fully updated, and the quick scan shows nothing, I am still running a full scan. I was also recently afflicted by opt_content.js. These problems appear to stem from a download from CNET (who I usually trust) of Harry's Photo Filters, which also installed a bunch of crap into my browsers. So far there is no record of this threat on Norton. A search of the community doesn't come up with this, though it is recognized by Spybot.
One of the symptoms is that the browser opens new windows randomly. The windows appear to be legitimate websites, and vaguely related to the content I was attempting to access, but bears no relationship to the buttons I was clicking.