Analysis of information sources in references of the Wikipedia article "Black operation" in English language version.
For most of the Soviet period, the undercover work of the secret police was directed at [...] potential enemies of the state. Particularly in the Stalinist period, a vast network of informers existed throughout the country [...]. Although approximately one out of ten individuals were acknowledged informers, most of the population was compromised in some way through their cooperation with the secret police.
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