Joseph McElroy, who was instead ordered to serve a 200-hour community punishment order, bypassed the facility’s electronic security systems with sophisticated software he had developed and nicknamed Deathserv.

The 16-year-old wanted to use the advanced network’s power to download and store films and music from the internet.

London’s Southwark Crown Court heard that once he had succeeded, he used a special password to protect his collection and cover up his “parasitic” invasion.

But his need to share his success with fellow hackers proved to be his downfall.

So many of them also accessed the system at the Fermi National Accelerator Laboratory in Illinois – one of the world’s most foremost centres for high energy physics research – it began to slow down.

Technicians became concerned, discovered the breach and “pressed the panic button”.

Officers at Scotland Yard’s computer crimes unit were alerted and quickly traced the A-Level student to his east London home.

McElroy, now 18 and a first-year engineering undergraduate at Exeter University, pleaded guilty to one count of unauthorised modification of the contents of a computer between June 10 and 25, 2002.

Passing sentence, Judge Andrew Goymer told him he ought to “think yourself lucky” he was not going to prison.

“Computers are an important feature of life in the 21st century. Government, industry and commerce, as well as a whole variety of other institutions, depend upon the integrity and reliability of their computers in order their proper and legitimate activities can be carried on.”

As the slightly built, bespectacled defendant stood in the dock with his hands folded in front of him, the judge said no criticism whatsoever could be levelled at the way US authorities responded to the security breach.

“One can well understand why their initial reaction was to think that a terrorist attack had been made to compromise that computer.

“It caused a great deal of damage and expense amounting to �21,000 ($A50,270).

The judge said he had to think “long and hard” how best to punish McElroy for what was clearly a “serious” offence.

While “giving you the benefit of the doubt” and accepting that McElroy was initially unaware whose system he was hacking into, Parliament had intended such conduct be dealt with severely.

It was important the “wrong message is not sent out to anybody else who is tempted to behave in this way.

“Others with perhaps more sinister motives than you ought not to think they will get away with it lightly.”

However, said the judge, his previous good character, the fact that he had not caused any actual harm and had not accessed any classified material had helped persuade him prison was not necessary in this case.