i had a problem like this recently. there were a bunch of those boxes. it also added a toolbar to one of my browsers. it was nowhere in the add/remove programs; there WERE some folders in the "Program Files" folder that were tied to them, but when i tried to delete the specific folders, it just said "machine needs to be re-booted to finish removal" and when you re-boot, nothing changed. one of the pop-ups was to buy something called "virus-burst" and looking into that, i found there are a ton of malware-type files related to this one. there was a removal program called "smitrem.exe" that helped me find my way to removal...look up smitrem and virus burst on google, see if any of there descriptions match what you are getting. there was some work involved, had to re-start in safe mode and run a program that removed it entirely, but now all is well.

if this sounds like it'll help but you can't find anything using google, message me and i will try to find the exact website i found the removal prog on and send to you (i'm not on my home pc currently)

good luck!