A Briton accused of mounting the largest ever successful hack of U.S. government computer networks could be prosecuted as an “enemy combatant” under U.S. anti-terror laws, an expert witness told his extradition hearing Tuesday.

Gary McKinnon, 40, of London, is wanted in the United States over allegations that he illegally accessed 97 computers, including U.S. Army, Air Force, Navy and NASA systems, causing $700,000 in damages.