What does a search engine know about you?

What does a search engine know about you? Who knows it? And do they know it’s you?

It’s said that you can tell a person by the company he keeps or, in this case, by the questions she asks. The New York Times was able to identify a supposedly anonymous individual, three months of whose search history was made public by AOL.

But the detailed records of searches conducted by Ms. Arnold and 657,000 other Americans, copies of which continue to circulate online, underscore how much people unintentionally reveal about themselves when they use search engines — and how risky it can be for companies like AOL, Google and Yahoo to compile such data.

AOL has withdrawn the data, but copies are still available. A public discussion of the data is finding some interesting trends: Aside from the expected searches for porn, at least one searcher might be planning to murder some one.