Online hackers group Anonymous on Friday attacked the Greek justice ministry website in criticism of the country's tough fiscal reforms and its decision to join a controversial anti-piracy deal.

"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 said in a statement posted on the ministry's site.

"Democracy was given birth in your country but you have now killed it," they added.

Greece is applying a crunch economic overhaul under supervision from the European Union and the International Monetary Fund that has left nearly 900,000 jobless and plunged the country into a deep recession.

The hackers also threatened to "deface" media and ministry sites unless Athens withdraws from the Anti-Counterfeiting Trade Agreement (ACTA), a deal signed on January 26 to create international standards for intellectual property protection.

Greece was one of the 22 signatories among EU states. Critics of the agreement say it could significantly curtail online freedom.

"Next target will be all the media in Greece," the hackers warned.

"We have most of the media websites admin passwords," they added.

Greek police said they have launched a probe.

"The investigation is in process, we are examining the attackers' electronic traces," the police department said.