Richard Pryce, was only 16 when he used a basic pounds 750 computer from his bedroom in north London to infiltrate some of America's top security establishments.
Codenamed Datastream Cowboy, Pryce, now 18, was the subject of allegations in the United States Senate, where the unknown "spy" was accused of "causing more harm than the KGB" He has also been described as "The number one threat to US security".
But his solicitor insisted yesterday that it was a "schoolboy prank" and that the teenager with just six months experience had used information taken off the Internet to break into the US networks. Lawyers believe the case shows the extraordinary lax security deployed within US military systems.
Pryce was fined pounds 1,200 plus pounds 250 cost yesterday after pleading guilty to 12 charges of gaining unauthorised access to computer systems in March and April 1994. He has now dropped his interest in computers in favour of a double bass which he studies at the Royal College of Music in London.
The first that Pryce's parents, Nick and Alison, knew of their son's activities was when members of Scotland Yard's Computer Crime Unit arrived at the home in Colindale, north London, to arrest him.
Bow Street Magistrates' Court heard that Pryce managed to hack into the Grifiss Air Force Base in New York, where it is alleged he downloaded material about artificial intelligence and battlefield management systems. He also broke into the Lockheed Space and Missile Company, in California.
The systems he was said to have obtained access to included those for ballistic weapons research, and aircraft design, payroll, procurement, personnel records and electronic mail. The infiltration led to allegations that a spy had managed to infiltrate secret intelligence data.
His hacking was described as an example of a growing and serious threat to US national security in reports and testimony to a Senate committee by the US General Accounting Office.
Some of the more outlandish allegations about the effects of Pryce's hacking exploits were later seen as an attempt to obtain extra funding. Indeed, US officials later insisted that Pryce had been unable to access any secret information.
Despite these claims, it is understood that the British authorities were considering using a Public Immunity Certificate, a gagging order, to cover part of the hearing, but decided not to bother after the more serious charges were dropped.
Geoffrey Robertson QC, for the defence, said that what the Pentagon had at first suspected was a European spy-ring, it later discovered was a 16-year-old in north London. "He was riding, rather than surfing, the Internet. He made no profit and there was no subversion of defence systems," he said.