McKinnon's legal counsel expects to file a further appeal to the country's new Supreme Court, which begins operating in October, and perhaps to a European Union court.
McKinnon's extradition was approved by the British government in 2006 and McKinnon's legal representatives have been fighting to keep their client in the U.K. ever since.
McKinnon's mother, Janis Sharp, called the High Court's ruling a disgrace, according to a video posted online by the BBC. In the video, she asks for the support of President Obama to end the persecution of her son.
McKinnon has been diagnosed with Asperger's Syndrome, a form of autism, and has gained the support of a number of British celebrities and politicians who believe he will not be treated fairly in a U.S. court.
Having admitted that he broke into U.S. government computers, McKinnon maintains that he was motivated by the desire to expose UFO secrets that were being concealed.
In an interview with the BBC conducted after Britain's House of Lords rejected an appeal in 2008, McKinnon characterized his actions as a moral crusade. "[UFOs] have been reverse-engineered," he said. "Rogue elements of Western intelligence and governments have reverse engineered them to gain free energy, which I thought was very important, in these days of the energy crisis."
McKinnon's supporters characterize him as a harmless eccentric. And the number of people supporting his cause has risen, at least in the IT community. In 2006, Sophos, a U.K.-based computer security firm, found that 52% of the 565 IT professionals participating in an online poll believed that McKinnon should not be extradited. In 2009, 71% of 550 IT professionals surveyed felt that way.
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