McElroy is a first-year university student

"Hacking is still illegal and as a self-confessed serial hacker, McElroy and the hacker community at large will view this outcome as a green light to break the law."  --Ubizen

Joseph McElroy used the lab's computers for films and music taken from the net.

Southwark Crown Court waived a demand for £21,000 in damages as it ruled that McElroy could not pay the fine.

The June 2002 intrusion by the Exeter University student sparked a full-scale alert at the Chicago laboratory, which researches high-energy particles.

Fearing a terrorist attack, the computer was closed down for three days and the US Department of Energy, which oversees the safety of the country's nuclear weapons, sounded a full-scale alert.

'Green light'

The 19-year-old from east London had admitted hacking into the Fermi National Accelerator Laboratory.

He took advantage of a flaw in the lab's authentication system and used the company's network bandwidth to download and store hundreds of gigabytes of copyrighted film and music files.

Judge Andrew Goymer decided against sending McElroy behind bars as he had not accessed classified material on the network and had not intended to cause harm.

He told the student he ought to "think yourself lucky" he was not going to prison.

"Computers are an important feature of life in the 21st century," said Judge Goymer.

"Government, industry and commerce, as well as a whole variety of other institutions, depend upon the integrity and reliability of their computers in order that their proper and legitimate activities can be carried on."

The judge said it was important that the "wrong message is not sent out to anybody else who is tempted to behave in this way".

But security experts have expressed disappointment at the leniency of the verdict.

"The McElroy hacking case highlights an increasingly common practice in the online world - unfortunately for him, he picked the wrong bandwidth to steal," said David Williamson, director of sales at security firm Ubizen.

"It is very worrying that appropriate compensation or a custodial sentence has not been issued in this case.