A British man who allegedly crippled US defence systems in the "biggest military computer hack of all time" could be sent to Guantanamo Bay if he is extradited, his lawyer claims.

Edmund Lawson told Bow Street Magistrates Court in central London that Washington wanted "administrative revenge" on his client, Gary McKinnon, because he had exposed embarrassing weaknesses in its IT security.

McKinnon, who was described by his lawyer as a "40-year-old computer nerd", is wanted in the United States for allegedly infiltrating systems at the Pentagon, Army, Navy and space agency NASA from his bedroom in north London.