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.