Anonymous' hackers accessed the website of Greece's justice ministry, posting a message of protest against the EU and IMF-inspired austerity policies.
"You have introduced a new dictatorship upon your people's shoulders and allowed the bankers and the monarchs of the EU to enslave them both economically and politically," the group's message said. "You have joined the IMF (International Monetary Fund) against your people's acquiescence...democracy was given birth in your country but now you have killed it."
The hacktivists also criticised Greece for joining the international copyright deal called Acta, or Anti-Counterfeiting Trade Agreement, along with Poland and other European countries.
Last week, the Polish branch of Anonymous has attacked Polish government websites for the same reason, including the prime minister's office, leaving several paralysed.
Anonymous released a statement on Pastebin warning: "Polish government - we are more powerful than you. We have a lot of your files and personal information. We warn you to exercise caution."
Poland signed Acta in Japan despite huge demonstrations in Warsaw Street and the hacking of governmental website. Poland's Prime Minister Tusk insisted that his government would not "succumb to blackmail".
He posted a '10 myths about ACTA' article on its web site. PO says that ACTA is not a "secret agreement" as critics have suggested. PM Tusk's party also say the agreement is in line with international trade law, particularly the so-called TRIPS agreement (Agreement on Trade-Related Aspects of Intellectual Property Rights).
Demonstrators fear that Acta, which is to be ratified by the European Union, will be as pernicious as Sopa, the Stop Online Privacy Act which was withdrawn by the White House and the US Senate after a mass protest by hundreds of major user-generated content websites.