Anarchists and daredevils who declare themselves to be fighting for free access to the Zone, and consequently find themselves in constant conflict with army units, military stalkers, and Duty.
These freedom fighters believe that information about the Zone must not be hidden from humanity, and challenge the state's monopoly over the Zone's secrets and wonders.
I found out from the "free men" that the Zone has appeared as a result of military tests of a secret weapon. One stalker from "Freedom", nicknamed "Sly", has assured me that he knows that for certain. The information is precise and verified, he says.
I do not know if that is so, but it all fits together – the mysterious nature of the disaster, the military's interest in the Zone from the very first day of its creation, and their dislike of regular stalkers, and their attempts to get to the center – there where, as Sly says, that secret weapon is still located.