Mark Zuckerberg founded Facebook in his college dorm room six years ago. Five hundred million people have joined since, and eight hundred and seventy-nine of them are his friends. The site is a directory of the world’s people, and a place for private citizens to create public identities. You sign up and start posting information about yourself: photographs, employment history, why you are peeved right now with the gummy-bear selection at Rite Aid or bullish about prospects for peace in the Middle East. Some of the information can be seen only by your friends; some is available to friends of friends; some is available to anyone. Facebook’s privacy policies are confusing to many people, and the company has changed them frequently, almost always allowing more information to be exposed in more ways.
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