Thankfully, a colleague and friend of mine, George Chlapoutakis (also known as DarkSYN) got his hands on a genuine screenshot of the defacement containing the full message in the Greek language and proceeded to write an accurate translation.
The story sums up as follows:
The purpose of GST (or Greek Security Team's) intrusion was neither to disrupt the experiment, nor to humiliate the CERN admins.
Their statement was against their adversaries in the Greek underground scene and the only reason they chose this site was due to it's extraordinary traffic.
Link to Original Source