If you have anything to do with the internet, you leave fingerprints on almost everything you touch. Those who know what they are looking for will be able to know you almost better than you know yourself.

Once online, personal information is almost impossible to delete.

Even online pseudonyms are a flimsy veil.

personal revelation is the unspoken quid pro quo for using the social networking sites that are hugely popular among young people. "Users understand that privacy is important," he says. "But they also understand that letting go of privacy is important if you want to play the game. You can't get very far in online communities if you don't make at least some information available."

last year AOL released supposedly anonymous data about the web searches of 658,000 subscribers. Many could easily be identified: the words people Google the most, for example, are usually their own name.