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.
The Ministry for State Security (German: Ministerium für Staatssicherheit, MfS, German: [ɛmɛfˈʔɛs] (listen)), or State Security Service (Staatssicherheitsdienst, SSD), commonly known as the Stasi (German: [ˈʃtaːziː] (listen)),[n 1] was the official state security service of the German Democratic Republic (East Germany, GDR) from 1950 to 1990. It has been described as one of the most effective and repressive intelligence and secret police agencies to have ever existed.