"Social Networking (SN) has emerged as one of the most successful social and technological phenomena of the 21st century. User numbers have increased
rapidly since the first social networks emerged in 2004. MySpace and Facebook, for example, are widely visited websites with hit rates that are increasing rapidly.

As with many fast-growing technologies, security has not been the first concern. SN websites create a feeling of being amongst friends.  Millions of young people disclose intimate details of their personal lives but very few realize, for example, that a potential employer might one day discover these details. The risks of identity theft, extortion and spear-phishing are greatly increased due to the level of personal information that users readily provide with little or no protection."

http://www.enisa.europa.eu/doc/pdf/publications/enisa_quarterly_09_07.pdf

Urs