A Greek hacking crew has come close to getting into the controls of Cern's Large Hadron Collider (LHC), which went live on Wednesday.

The hackers managed to breach Cern's network defences and got into the Compact Muon Solenoid Experiment. There they left a file reading: 'GST: Greek Security Team. We are 2600 - don't mess with us.'

"There seems to be no harm done. From what they can tell, it was someone making the point that it was hackable," James Gillies, a spokesman for Cern, told The Daily Telegraph.

"It was quickly detected. We have several levels of network, a general access network and a much tighter network for sensitive things that operate the LHC."

The hackers were described as "one step away" from the computer control system of one of the huge detectors of the LHC, a vast magnet that weighs 12,500 tons, measuring about 21 metres in length and 15 metres wide.

"We think that someone from Fermilab's Tevatron [the competing atom smasher in America] had their access details compromised," said one of the scientists working on the machine.

"What happened wasn't a big deal. It just goes to show that people are out there always on the prowl."

Cern said that the centre had been deluged with calls and emails from members of the public, worried that the LHC would destroy the planet by creating a black hole, despite such claims being checked and rejected.