AOL found itself at the centre of an internet firestorm after its employees published details of the search histories of 658,000 of the group's US users.

The information, the release of which AOL itself yesterday called "a screw-up", was published on an AOL site aimed at academics and discovered by technology blogs on Sunday, some of which used the data to analyse search trends.

Although the individuals whose search histories were detailed were not identified by name, they each had a unique user number.

Bloggers, picking up on the date, noted the search history for one user, which showed that the individual conducted a number of searches for "how to kill your wife" and was also keen to find images of "dead people", "car crashes" and "decapitation".

By the time AOL, the internet group owned by Time Warner, became aware of the breach and took the information down, the data was widely copied and is still easily available on the web.

"This was a screw-up and we're angry and upset about it," AOL said in an e-mailed statement.

"It was an innocent enough attempt to reach out to the academic community with new research tools but it was obviously not appropriately vetted and if it had been, it would have been stopped in an instant."

The revelations come at a sensitive time for AOL. The pioneer of internet access took over Time Warner at the height of the internet boom in 2001 but, since then, the collapse in its value has meant there have been constant questions about its future.

Last week, AOL and Time Warner announced a plan aimed at finally turning the group into a valuable business that could lift Time Warner's share price.

From September, AOL's remaining 18 million paying customers will receive their AOL e-mail addresses and software for free. The resultant loss of billions of dollars of subscription income is expected to be offset by sharp cost cuts, including 5,000 job losses, and a bigger share of the online advertising market.

Analysts said the biggest risk was that AOL would not be able to execute the new plan - a view that could be reinforced by the release of the data that suggests a lack of controls.

The move will raise fresh concerns about the safety of the information stored about individuals.