It’s a real arrest and not simply a detention.
There’s no more info atm.
Translated from Greek: http://athens.indymedia.org/front.php3?lang=en&article_id=1068699
Translator’s comments: we see how simply expressing your solidarity to a persona non grata in Greece can land you in a police station with cops over your head. That’s Greece where anyone who deviates from the mainstream role of consumer–worker is repressed and labelled a terrorist and an ‘enemy of democracy’.