Let me share with you the paper “A study of malicious attacks on Facebook” presented by Robert Sandilands during the event VB2011 that was held from October the 3rd till the 7th in Barcelona, Spain.
A well made summary on the main attacks on a social network widely used around the world but also widely used by malware writers for spreading malicious content.
http://blog.commtouch.com/cafe/data-and-research/a-study-of-malicious-attacks-on-facebook/