In May 1943, Ernst Kaltenbrunner, the new head of the Reich Central Security Office, gave Hitler a report describing in detail the organization of the French Resistance. Indeed, during the Second World War, most of the Resistance networks had been infiltrated by traitors, the "V Man" (trusted men) in the service of the occupier. The Germans had established treason as a system and recruiting Frenchmen ready to inform on them was one of their priorities. It was these Frenchmen, whose number is estimated at between 20,000 and 30,000, who dealt terrible blows to the Resistance.