Details are emerging of security leaks at the White House which have shut down an internet spying operation that had successfully cracked al-Qaeda's computers.

Reports suggest that the latest video from Osama Bin Laden was found online before its release by the Search for International Terrorist Entities Institute (Site Institute), which had infiltrated al-Qaeda's intranet, known in intelligence circles as 'Obelisk'.

The Site Institute then passed the details on to contacts in the White House, with a link to the new video on the Site Institute website and a transcript of the contents. Also included was a request to keep the information secret.

Government-registered computers began downloading the video within 20 minutes, and dozens of government computers went onto the website for copies over the next three hours.

By that afternoon Fox News and other stations were broadcasting sections of the video, including screen shots of the website and mentioning the Site Institute's name. Within an hour of the publicity al-Qaeda's intranet was taken offline.

"Techniques that took years to develop are now ineffective and worthless," Rita Katz, Site's founder, told the Washington Post. "The US government was responsible for the leak of this document."

The Site Institute was set up in the wake of the 11 September attacks and is a not-for-profit organisation that is widely respected n the intelligence community.

The effects of the leak on its ability to monitor terrorists sites has severely weakened attempts to find out more about potential terrorist operations.

Fran Townsend, assistant to the president for counterterrorism and homeland security, has promised an investigation.

"We will learn more as time goes on, but I understand that the link to the Site was provided to the intelligence community, and the concern was that that link is the piece that was the thing that was made public," Townsend said in a press conference.

"So, as I say, I mean, obviously, I'm not - we here at the White House are unable to conduct an investigation, and I leave this to the Director of National Intelligence to ascertain the appropriate way of dealing with this and understanding what happened, so we can ensure it doesn't happen again."