A UFO enthusiast accused of the "biggest military hack of all time" lost his appeal to the Law Lords against extradition to the United States today.
Gary McKinnon, an unemployed 42-year-old, faces up to 70 years in prison if convicted in the US of sabotaging vital defence systems.
The House of Lords rejected a plea by McKinnon, who was never charged in Britain after admitting accessing 97 US military and Nasa computers, to quash an extradition request granted to the US authorities in 2006.
Lawyers for McKinnon, from Enfield, north London, pointed out that he could be sent to Guantanamo Bay as a terrorist suspect - despite his insistence that he accessed Pentagon computers looking for information about UFOs.
From the bedroom of his girlfriend's aunt's house in north London, he hacked into 97 American military computers at the Pentagon and Nasa between 2001 and 2002.
McKinnon never denied that he wandered around the computer networks of a wide number of US military institutions.
But he has always maintained that he was motivated by curiosity and that he managed to get into the networks only because of lax security.
American authorities claim he stole 950 passwords and deleted files at Earle naval weapons station in New Jersey.
He was accused of using his computer skills to gain access to 53 US Army computers, including those used for national defence and security, and 26 US Navy computers, including those at US Naval Weapons Station Earle in New Jersey, which is responsible for replenishing munitions and supplies for the deployed Atlantic fleet.
He was also charged with hacking into 16 Nasa computers and one US Defence Department computer.
Mark Summers, an official representing the US government, previously told a London court that Mr McKinnon's hacking was "intentional and calculated to influence and affect the US government by intimidation and coercion".
McKinnon lost his case at the High Court last year and went straight to the highest court in the land, the House of Lords, last month.
There David Pannick QC, representing him, said his extradition would be an abuse of proceedings.
McKinnon had been warned by the US authorities that he faced a life sentence rather than a couple of years in jail unless he agreed to plead guilty and accept extradition.
Without cooperation, said the authorities, the case could be treated as one of terrorism. It has been reported that US prosecutors wanted to "see him fry".
McKinnon said he was motivated by curiosity and was looking for evidence that the US government had information on UFOs.
His supporters say he is being made a "scapegoat" for security shortcomings on US military networks.
McKinnon described his exploits as "ridiculously" easy.
After a previous hearing, he said: "I was amazed at the lack of security and the reason I left not just one note but multiple notes on multiple desktops was to say 'Look, this is ridiculous'.
"My intention was never to disrupt security. The fact that I logged on there and there were no passwords means that there was no security."
A statement by solicitors for McKinnon, who was not at the House of Lords today, read: "Gary McKinnon is neither a terrorist nor a terrorist sympathiser.
"His case could have been properly dealt with by our own prosecuting authorities.
"Instead, we believe that the British Government declined to prosecute him to enable the US government to make an example of him.
"American officials involved in this case have stated that they want to see him 'fry'.
"The consequences he faces if extradited are both disproportionate and intolerable and we will be making an immediate application to the European Court to prevent his removal."