I remove this crap for a living, and I've seen the scam up close.
When the victim pays, the scareware purveyor removes most of the program... which "fixes" the PC. They leave behind a back door, and Registry entries making the machine download .exe files without prompting, but they mostly stop bombarding the victim with warnings... for a month or two.
Then, they attack again, trying to get more money. I've had a few customers who paid for the first attack, then finally called for help when they got hit again; it was easy to see what the first program did, and track down the quick site redirect that brought on the second infestation.
The real criminals here: Visa and Mastercard, for maintaining merchant accounts for these scumbags. Brian Krebs exposed this, and got it shut down... for two weeks or so, and they've back ever since without interruption.