A British hacker who broke into US military computers is set to be extradited to the US after the highest British court dismissed his appeal today.

Gary McKinnon, of north London, will be the first person to be extradited to the US for computer-related crimes, after he was accused six-and-a-half years ago.

McKinnon, aged 42, said he plans to appeal the decision to the the European Court of Human Rights, the last appeal he can file. If convicted, he could face up to 60 years in prison.

McKinnon maintains that his hacking never caused any harm, and that he only probed the computers looking for evidence that the US government has knowledge of UFOs.

However, the US said that the intrusions disrupted computer networks used by the military that were critical to operations conducted after the September 11, 2001, terrorist attacks. The US estimates the damage caused by McKinnon at $700,000.

In his appeal McKinnon argued that when US prosecutors offered him a shorter sentence in return for a guilty plea, that offer put disproportionate pressure on him to surrender his legal rights and particularly his right to contest extradition¨. Pressure of that kind, he argued, runs counter to English law.

But in their judgement, the Lords of Appeal said: "The difference between the American system and our own is not perhaps so stark as the appelant's argument suggests. In this country too, there is a clearly recognised discount for a plea of guilty."

US prosecutors had said that in return for pleading guilty to two counts of fraud and related activity in connection with computers, McKinnon could be sentenced to as little as three years in prison, of which he would likely serve only 6 to 12 months in a US prison before returning to the U.K. to serve the rest of the sentence.

An equivalent offence committed against a target in the UK could have got him life imprisonment, the Lords of Appeal said. "The gravity of the offences alleged against the appelant should not be understated."

McKinnon had admitted to using a program called "RemotelyAnywhere" to hack into PCs in the US late at night when employees were gone. His hacking exploits started to unravel after McKinnon miscalculated the time difference between the US and the UK, and one employee noticed a PC acting oddly.

The US pursued extradition for the offences, which McKinnon sought to block. The then-UK Home Secretary John Reid approved the extradition order, but McKinnon appealed. He lost that appeal in London's High Court in April 2007.

McKinnon then turned to the House of Lords, the final today.

See also:

House of Lords to hear UK NASA hacker's case

UK hacker extradition appeal hearing begins