One of the Stasi's main tasks was spying on the population, primarily through a vast network of citizens-turned-informants, and fighting any opposition by overt and covert measures, including hidden psychological destruction of dissidents (Zersetzung, literally meaning "decomposition"). It arrested 250,000 people as political prisoners during its existence.[9] Its Main Directorate for Reconnaissance (Hauptverwaltung Aufklärung) was responsible both for espionage and for conducting covert operations in foreign countries. Under its long-time head Markus Wolf, this directorate gained a reputation as one of the most effective intelligence agencies of the Cold War. The Stasi also maintained contacts, and occasionally cooperated, with West German terrorists.