There seems to be a virus on the loose that has been picking up steam since April that can alter the way your Windows box revalidates. The virus is said to take control of the system and will ask you for your credit card information. Any attempt to cancel the process will result in a full shut down.
"You can only choose only Yes or No," Takashi Katsuki wrote on the Symantec security Weblog. "You can't run Task Manager or any other applications. If you choose No your PC will be shut down immediately."