A UFO enthusiast who hacked into top-secret US military computers appealed to the Home Secretary yesterday to stop his extradition after losing a legal appeal.

Gary McKinnon is due to be extradited to the United States within two weeks and could face a sentence of up to 80 years in a maximum-security prison if found guilty. He admits to having accessed 97 US Navy, Army, Nasa and Pentagon computers in what has been described as “the biggest computer hack of all time”.

Mr McKinnon, 42, an unemployed systems analyst, has said that he was looking for computer files containing details about UFOs and aliens. The US Government says that he stole passwords, deleted files and left threatening messages.

Mr McKinnon, of Palmers Green, North London, admitted carrying out the hacks using a computer in the bedroom of a house owned by his girlfriend’s aunt. He says that he was motivated by curiosity and gained entry only because of lax security.

He had asked the European Court of Human Rights to stay his extradition pending an appeal, but the application was refused yesterday. He lost appeals to the High Court last year and to the House of Lords last month.

US prosecutors allege that he caused nearly $1 million (£550,000) in damage. The US military says that he rendered 300 computers at a US Navy weapons station unusable immediately after the September 11 attacks.

Mr McKinnon had become obsessed with a theory that the US was using alien technologies to create weapons and “free energy”. He gave up his job and spent hours every night hacking in search of evidence.

He hacked into 53 US Army computers 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 Atlantic Fleet. Calling himself Solo, he left a threatening message: “US foreign policy is akin to government-sponsored terrorism these days? It was not a mistake that there was a huge security stand-down on September 11 last year . . . I am SOLO. I will continue to disrupt at the highest levels.”

He was caught in November 2002 as he tried to download a grainy black-and-white photograph that he believed was of an alien craft held on a Nasa computer in the Johnson Space Centre in Houston, Texas. He was easily traced by the authorities because he used his girlfriend’s e-mail account.

Mark Summers, an official representing the US Government, said that Mr McKinnon’s hacking was “intentional and calculated to influence and affect the US Government by intimidation and coercion”.

If extradited, Mr McKinnon faces trial on eight charges of computer fraud. Each charge could carry a sentence of ten years in jail and a $250,000 fine. It is likely that he would receive a much lighter sentence and that, under a plea bargain offer, he would spend six to 12 months in a US jail before being returned to Britain to serve the rest of his sentence.

Mr McKinnon has previously said: “What I did was illegal and wrong, and I accept I should be punished. But I am not a member of al-Qaeda. I believe my case is being treated so seriously because they’re scared of what I’ve seen. I’m living in a surreal, nutter’s film.”

He has suggested that the US authorities should take advantage of his expertise rather than prosecute him. “The reason I left not just one note, but multiple notes on multiple desk-tops, was to say ‘Look, this is ridiculous’.”

Karen Todner, from Kaim Todner solicitors, said that Mr McKinnon was “distraught” about the decision by the European Court of Human Rights and appealed to Jacqui Smith, the Home Secretary, to intervene. “He is terrified by the prospect of going to America,” she said.

Ms Todner added that the alleged offences had been committed on British soil and so he should be tried here. She also said that Mr McKinnon had recently been found to have Asperger’s syndrome.

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