That sounds familiar... a guy I know had something similar once... he just clicked on the webpage where
some wallpapers were for download, and BANG he had such a thing installed... in his case it was even more "funny": Since then all texts in HTML pages which referred to certain keywords ("Software", "Hardware", "Mail", "Anime", "Wallpapaper",...) linked to some webpage of the spammers (providing "search functionality" there). Google was turned nearly unusable by this, as you could not click anymore on links which contained one of the keywords, as then only the link for the useless "search page" came through... In the end I had a look at the system together with the poor guy and in the end we managed to murder the crap again from his system.
Sometimes I REALLY wonder why they still use Windows in Business. The security risk (and the annoy-factor and the timeloss) with all that Adware stuff is soooo much bigger than any "advantage" (which many people would find argueable anyways...) of it can ever be... I guess they just use it as they "always did use Windows before".
Steffen