A group of men in camouflage crawl through dense forest, armed with Kalashnikov assault rifles and handguns. Balaclavas obscure their faces. They come to an abandoned building where they duck down and get ready. “Attack!,” one shouts, and throws a smoke-bomb towards the building. Then another group of armed men bursts from inside the building, their guns blazing.

It’s not an action-movie, but a clip from an amateur video of friends playing a combat-style game near the city of Penza, about 300 miles southwest of Moscow. They were playing a game called “Airsoft” or “Strikeball.” It’s a bit like paintball except that players use small plastic pellets or BB rounds. It is both very popular in Russia and legal.

What the men also had in common — apart from their interest in wargaming — was that they were members of a loose circle of left-wing, anti-fascist activists.

But according to Russia’s FSB intelligence service, they are “radical anarchists” who are members of a previously unheard of terrorist group called the “Network.” And the Penza Airsoft gathering was a training session for a conspiracy to bomb the World Cup and this year’s presidential elections — with the goal of stirring “armed rebellion.”