How Privacy Vanishes Online

Yet people often dole out all kinds of personal information on the Internet that allows such identifying data to be deduced. Services like Facebook, Twitter and Flickr are oceans of personal minutiae -- birthday greetings sent and received, school and work gossip, photos of family vacations, and movies watched.

Computer scientists and policy experts say that such seemingly innocuous bits of self- revelation can increasingly be collected and reassembled by computers to help create a picture of a person's identity, sometimes down to the Social Security number.

“Technology has rendered the conventional definition of personally identifiable information obsolete," said Maneesha Mithal, associate director of the Federal Trade Commission's privacy division. “You can find out who an individual is without it."