It appears that I had a VX2 variant of the adware on my computer. It was designed not to be detectable by any current spyware/adware detection programs. If you have this and can’t remove it, check out Lavasoft’s Ad-Aware with VX2 Cleaner plugin. Once I used the plugin, I was able to get rid of the pop-up ads.
I can’t believe that these people are legally allowed to do this. It ought to be considered trespassing. Then again, I don’t know who did it, so pressing charges would be very difficult.