Short answer: Malware.
Whether it came from the manufacturer or not is irrelevant really. Everyone would recommend something different but in your case, pick any Anti-malware tool (Ad Aware by Lavasoft is a good start) and run it.
Drastic measures below this point. Read only if desperate.
Don't know if you have the capability or not, but you coule just nuke the site from orbit. It's the only way to be sure. That means reload a fresh non-vendor specific windows on the station. It's really drastic, but you're only 2 weeks in. I could be wrong but I would imagine that you have little more than system preferences and a few apps installed.
A tactical nuke (read: less drastic) would be to factory reset. Most vendors these days are doing the next best thing and restoring from an image.
I've seen people putz around for days and weeks trying to clear something like this out in an effort to save a little bit of data, when an afternoon of data copy + reinstalling would have taken care of it.