Greek police said Monday they had arrested an 18-year-old suspected of hacking into the justice ministry's website earlier this month, an attack claimed on behalf of online hackers group Anonymous.
Two other boys aged 16 and 17 were also being sought over the case, police said.
In the February 2 cyber attack, the hackers posted a statement on the ministry website in response to Greece's tough fiscal reforms and the country's decision to join a controversial international anti-piracy pact.
"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 statement said.
"Democracy was given birth in your country but you have now killed it."
The hackers had also threatened to "deface" media and ministry sites unless Athens withdraws from the Anti-Counterfeiting Trade Agreement (ACTA), which was signed on January 26 to create international standards for intellectual property protection.
Greece was one of the 22 signatories among European Union states.
Critics of ACTA say it could significantly curtail online freedom and a number of European countries have said they will now freeze their ratification of the accord.
"Next target will be all the media in Greece," the hackers said, warning: "We have most of the media websites admin passwords."
The three youths have been linked to dozens of cyber attacks against Greek websites, using the alias Greek Hacking Scene and the nicknames "delirium", "nikpa" and "extasy", police said.
They face at least a year in prison if convicted.
Greece has imposed tough budget cuts to try to win a new bailout deal from the EU and the International Monetary Fund but the measures have left over a million people out of work and plunged the country into a deep recession.
Explore further: Hackers hit Greek ministry over austerity, anti-piracy deal