number of occasional informers brought up the total to 1 per 6.5 persons. People in East Germany were subjected to a variety of techniques, including audio and video surveillance of their homes, reading mail, extortion, and bribery. International surveillance The West German intelligence agency Bundesnachrichtendienst (BND) employed approximately 10,000 East Germans as spies. The US National Security Agency (NSA) built one of its largest listening stations on top of Teufelsberg hill in the British sector of West Berlin, allegedly part of the global surveillance network ECHELON. "The Hill", as it was known colloquially, began operation in July 1961. A large structure was built atop the hill, which would come to be run by the NSA (National Security Agency). Construction of a permanent facility was begun in October 1963. The station continued to operate until the fall of East Germany and the Berlin Wall, after which the station was closed and its equipment removed. However, the huge buildings and massive radar domes still remain in place. Reunification and aftermath On 3 October 1990, the states of East Germany formally joined the Federal Republic of Germany to reunite East and West Germany. As a result of the revolution, Stasi files fell into the hands of the reunited German government. The Federal Commissioner for the Stasi Records was formed to control those files. See also Mass surveillance in Australia Mass surveillance in Russia Mass surveillance in the United States Mass surveillance in the United Kingdom References External links East Germany History of East Germany -