The activist hacker group Anonymous said it had taken down a number of Greek government websites on Monday, on the eve of a visit by German Chancellor Angela Merkel that is likely to be met by angry protests.
Several government websites appeared to go down briefly late on Monday, including those of the Citizens Protection Ministry, the police and the Ministry of Justice. A message appeared saying: "The page cannot be found".
Police could not confirm who was responsible for the attack, which Anonymous claimed in a series of Tweets on the social media site Twitter.
In a message posted on YouTube, the group criticized the huge security operation that police plan for Tuesday to contain protests against Merkel, comparing the government to the military junta that ruled Greece from 1967 to 1974.
Trade unions and opposition political parties have called for mass protests to greet the German chancellor, whom many Greeks accuse of unfairly forcing them down the path of painful austerity and driving the country even deeper into recession.
The Greek government is locked in negotiations with its international lenders on yet more spending cuts to clinch the next tranche of a 130-billion-euro ($169-billion) bailout saving the country from bankruptcy.
Anonymous in February claimed a cyber-attack on the Greek ministry of justice website. ($1 = 0.7711 euros