A previously unheard-of group calling itself “Deviant Behaviors for the Expansion of Revolutionary Terrorism International Revolutionary Front” claimed responsibility late on Friday for a bomb attack on the headquarters of Microsoft in Maroussi, north of Athens.

In a nine-page proclamation, uploaded onto an anarchist website, the group claimed responsibility for driving a van packed with gas canisters through the glass facade of the company’s offices before setting the vehicle alight, causing an explosion that wreaked major damage but no injuries.

The document calls Wednesday’s attack “an act of war against the sinister silence and generalized captivity,” and expressed support for militants detained in Greece and Italy. It also mentioned Ted Kaczynski, the so-called “Unabomber” who conducted a mail bomb campaign in the US.

The police’s counter-terrorism unit was examining the authenticity of the proclamation.