Koobface first hit the social networking site last year. All the attacks have sought to steal personal information from Facebook users, over and above what they actually want to release on the public boards.
Once installed, this application then tries to re-send itself to every contact of the victim.
One of the problems Facebook faces is that developers are currently allowed to issue apps on the network without being security checked. Whilst this open development is an asset in many ways, it causes the problems the network has faced in the last few days.