The next time someone tries to “friend” you on Facebook, it may turn out to be an undercover fed looking to examine your private messages and photos, or surveil your friends and family. The Electronic Frontier Foundation has obtained an internal Justice Department document that describes what law enforcement is doing on social networking sites.
The 33-page U.S. Justice Department document shows that law enforcement agents from local police to the FBI and Secret Service have been logging onto MySpace and other sites undercover to communicate with suspects, read private postings and view photos and videos that are restricted to a user’s friends.
source : http://dillsnapcogitation.wordpress.com/2010/03/17/facebook-fed-friends-go-undercover-to-keep-america-safe/