AOL has apologised after “mistakenly” releasing the search histories of around 650,000 users onto the web.

The internet giant has come under fire in the past week after its research division made public around 20 million keyword searches performed by its subscribers. Although the information didn’t include users’ names, the move has attracted widespread criticism that the company had breached their privacy and left them open to ID theft.

Although AOL has since removed the data from the web, blogs such as TechCrunch say the data had already been downloaded several hundred times.

The company said it had launched an internal investigation into what had happened – but said the move wasn’t cleared through official channels.

This was a screw up, and we’re angry and upset about it,” Andrew Weinstein, an AOL spokesman told Reuters.

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.”

Although a legal expert told the news agency that the incident did not violate AOL’s privacy policy as the data did not include personally identifiable information, bloggers have pointed out that users often search for their own names. At least one mirror site, which is still live at the time of writing, was set up before the data’s removal, according to TechCrunch.

Combine these ego searches with porn queries and you have a serious embarrassment. Combine them with “buy ecstasy” and you have evidence of a crime. Combine it with an address, social security number, etc., and you have an identity theft waiting to happen,” said TechCrunch’s Michael Arrington. “The possibilities are endless.

Ari Schwartz, deputy director of the Center for Democracy and Technology, told AP: “We’re glad to hear that AOL is treating this as a serious incident because it is a serious incident.