Last Tuesday, December 4th, a Golden Dawn office near Athens was bombed around 4 in the morning. The explosive used was dynamite, and it made quite the mess.
On March 19, 2010, a similar bomb was detonated in the fifth floor office of Golden Dawn, in downtown Athens. The bombing was announced twenty-five minutes prior to a local newspaper, resulting in the evacuation of the surrounding area.
Attacks like these are widespread and under reported in the media. While bombings are infrequent, assault and other forms of intimidation are widespread.
An important part of the far-left terrorist platform is a group of annalists who gathers information about nationalists and nationalist organizations, often quite openly. This information in turn is made available to a large group of activists, with the intended goal for radical action to be taken. This group of annalists has never faced prosecution as far as I know, and there is no political pressure to do much about them as the attacks are small with minimal collateral damage.
The far-right has occasionally tried to employ this tactic, but the system is quick to respond to intimidation from the right.