Presenting its latest report in Brussels, the anti-corruption group also warned that a lack of political accountability across the EU, but especially in southern Europe, had led to a rise in populism.
Managing Director of Transparency International Cobus de Swardt said: "The most powerful way to deal with populism, in the way that we see it emerging at the moment, is indeed for dramatically more accountability. If you look at countries such as Greece, more than 80% of Greek citizens say they have no trust in the political system or in political parties. In that environment, all forms of extremism will obviously flourish."
Along with Greece: Transparency International also named Italy, Spain and Portugal - the eurozone's most financially troubled countries - for having the worst problems inside their public administrations.