The worm uses social engineering to spread. It sends users bogus messages posing as an invitation to watch a video and prompts the user to download malware disguised as an Adobe flash plugin.
It is unclear what the purpose of the worm is. Its effects on an infected computer seem to be more annoying than destructive, so I suspect it’s laying the groundwork for a botnet farm, but that’s just a guess.
Here is the story from the Washington Post. The story also warns against two rogue pieces of malware that pose as Facebook apps.
Koobface is a Windows Trojan.