Marc Pampols

A Greek group of hackers attacked the CERN's website and displayed a page with the text "‘GST: Greek Security Team.'"

The hackers did not arrived at the level of the LHC control, but they where "one step away"

Here is a screen capture of the attack (click to see a large version)

Greek hackers attack the CERN

More information at the Telegraph

Here is a nice video from BBC Horizon podcast, that explains how the CERN's LHC (Large Hadron Collider) works: