Reboot and run a virus scan immediately.

I was looking up dumpster rental companies to deal with some impending remodeling debris, and one of their sites had been hacked, and I got the exact same thing happening - a butt-ton of freak IE pop-ups even though I was using Firefox, my desktop had been hijacked, and I kept getting offers to install & run a spyware checker.

So, I pulled my wireless adapter out and did a shutdown & restart. When I ran a virus check, sure enough, there was fresh unpleasantness in my D: drive.