Just because a "friend" sends you a picture of a hot girl on Facebook or MySpace does not mean you should open it, because that "friend" may be part of a botnet, according to Kaspersky Lab.
Basically, infected machines are spreading the worm by sending messages to all of your social networks’ friends list; linking to video clips and they prompt the recipient to download a file that claims to be the latest version of Flash.
Those infected who then log onto their profiles next time will then allow the worm to spread. The new worm comes in two variants, Networm.Win32.Koobface.a and Network.Win32.Koobface.b. Variant A affects MySpace users, while Variant B affect Facebook users.