Gary McKinnon could face up to 70 years in a US prison
British computer hacker Gary McKinnon has lost the latest round of his battle against extradition to the US.
The Crown Prosecution Service refused to bring charges against him in the UK.
Mr McKinnon, 42, from Wood Green, north London, faces up to 70 years in prison if found guilty in the US of breaking into military computers.
His lawyers appealed for him to be prosecuted in the UK on lesser charges, but the CPS said the best place for the case to be heard was the US.
Glasgow-born Mr McKinnon has always admitted hacking into the computer systems in 2001-2 - which the US government says caused damage costing $800,000 (£550,000).
In total, he hacked into 97 government computers belonging to organisations including the US Navy and Nasa.
Mr McKinnon has always said he had no malicious intent but was looking for classified documents on UFOs which he believed the US authorities had suppressed.
He has signed a statement accepting that his hacking constituted an offence under the UK's Computer Misuse Act 1990.
Gary is a gentle man with Aspergers - not a dangerous terrorist
Janis Sharp, Gary McKinnon's mother
The CPS said it found enough evidence to bring charges against the hacker under the act for obtaining "unauthorised access with intent".
But Alison Saunders, head of the CPS organised crime division, said: "The evidence we have does not come near to reflecting the criminality that is alleged by the American authorities."
She added: "These were not random experiments in computer hacking, but a deliberate effort to breach US defence systems at a critical time which caused well-documented damage.
"They may have been conducted from Mr McKinnon's home computer - and in that sense there is a UK link - but the target and the damage were transatlantic.
"The bulk of the evidence is located in the United States, the activity was directed against the military infrastructure of the United States, the investigation commenced in the United States and was ongoing, and there are a large number of witnesses, most of whom are located in the United States."
'Years of agony'
Mr McKinnon's mother, Janis Sharp, said she was "heartbroken by the lack of compassion" shown towards her son.
"Gary is a gentle man with Aspergers - not a dangerous terrorist.
"His obsessions led him to search US computer systems. Wrong, yes, but extraditing him to a high-security prison knowing he won't survive - surely no-one can honestly believe that punishment fits the crime?
"We've suffered an agonising seven years which has ruined the lives and health of my family."
Mr McKinnon, who was arrested by British police in 2002, has already appealed unsuccessfully to the House of Lords and the European Court of Human Rights to avoid extradition.
His battle now rests on a judicial review of the government's decision to extradite him.
Last August, Mr McKinnon was diagnosed as having Asperger's Syndrome and his lawyers said he was at risk of suicide if extradited.