A British man with an obsession with UFOs who is accused of being the "biggest military computer hacker of all time" has lost his battle to avoid extradition to the United States.

Gary McKinnon, 41, an unemployed computer systems administrator, is wanted for allegedly gaining access to 97 American military and NASA computers between 2001 and 2002. He is accused of causing nearly $700,000 (£350,000) worth of damage by hacking into systems across the United States.

Officials claim that one intrusion shut down the network that serves the military district for Washington for three days. They say that he deleted computer files at a Naval Air Station, compromising security at a crucial time shortly after the September 11 attacks.

Mr McKinnon was first arrested in 2002, but a drawn-out extradition process meant that his case did not reach court until 2005. His lawyers claim that he could face up to seventy years in jail and at one point it was suggested that he could be sent to Guantanamo Bay, Cuba.

John Reid, the Home Secretary, granted the American request to extradite Mr McKinnon for trial, but his supporters have argued that the move would breach his human rights, as they say he has been subjected to “improper threats” including a comment from a New Jersey prosecutor that he would “fry”. There has not been an execution in New Jersey for 20 years.

It is very rare for the United States to request the extradition of someone accused of a cyber-crime. The fact extradition was requested at all, suggests that they are taking this case extremely seriously.

Mr McKinnon, who has described himself as a “bumbling computer nerd” has spoken in interviews of a quest to use his computer skills to uncover evidence of UFOs (Unidentified Flying Objects) and other spacecraft, that he believed the US government was concealing. He says his motives were not malicious and has claimed that the American systems he came across lacked firewalls and basic password protection.

The Briton has a vocal support network, whose members say he is being made a scapegoat for American security failings. Supporters contribute to a blog, have signed petitions and created a website pushing for him to be tried on home soil.

Within minutes of this morning’s decision, comments and messages of support had been posted. One contributor, Louis Berk, wrote: “A naive man perhaps, but certainly not a dangerous one. I cannot understand what purpose can be achieved by submitting him to the US justice system. This is a travesty of justice regardless of the side of the Atlantic you come from.”

In court this morning Lord Justice Maurice Kay and Mr Justice Goldring said: “We do not find any grounds of appeal”, and dismissed McKinnon’s legal challenge.

However, Ben Cooper, appearing for Mr McKinnon, said a bid would now be made to appeal the case to the House of Lords, the highest court in the land.

Mr Cooper said: “We will certainly be applying for this court to certify a point of law of public importance and to grant leave (for the final appeal to the law lords).”

He also indicated that McKinnon had been suffering from ill health during recent court hearings and was still receiving treatment from doctors.

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