According to a USA Today report Facebook users are being targets for distribution of a nasty version of the Koobface worm that uses a wall page invitation to watch a cutesy Christmas video to take over the user's computer.
PandaLabs researcher Sean-Paul Correll says when the victim clicks on the link there's a Windows warning message requiring them to solve a CAPTCHA puzzle within three minutes.
If the puzzle goes unsolved after three minutes, the PC freezes. Rebooting won't help. The CAPTCHA puzzle will reappear. The only way to end the loop is to solve the CAPTCHA. The victim can then use his or her machine as normal. But the attacker still has control.
Read the full report at the USA Today Web site.