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For example, a banner advertising a film could come with a quote from a user's friend who recently watched and wrote a positive comment in their profile about it.

The system decides close friends by monitoring the number of messages sent between users, and the interaction between people on applications in Facebook.

SocialMedia Networks describes this technology as FriendRank, and claims it works in much the same way as Google's PageRank which analyses the importance of links between web pages.

While Facebook has tried to capitalise on its huge user base with its Beacon advertising tool, the privacy implications caused a backlash amongst the Facebook user community.

Similar technology is being developed by rival 33Across, though it seems likely both companies are set to endure the same privacy furore as Beacon.