How significant was the role of the secret police in maintaining communist control in the years 1917-85?

This question is a breadth question asking a student to assess changing significance of aspects of communist control. Secret police is the example given in the question and therefore must be used. Other factors may include: art, media (or specific elements of media), control of religion or the influence of personality cults.Throughout it's various guises, the secret police saw a general decline in power between 1917-85. During Stalin's reign the secret police, NKVD, had significant power that partially facilitated his cult of personality. Terror was used excessively to create a totalitarian state and government obedient to Stalin. However, de-Stalinisation and international scrutiny in the Cold War, saw the secret police - now the KGB - vastly decline in its powers and therefore significance. Despite this, it remained the most effective method of control.Other forms of control saw vastly declining significance, even facilitating dissident activity. For example media, where radio particularly facilitated non-comformist action, with radio stations like Voice of America being broadcasted into the USSR. Previously, Stalin had a tight grip over censorship and had exploited radio and the illiterate population as means of indoctrination. On an arts and culture front, Khrushchev's cultural thaws allowed the birth of stilyagi. Stilyagi was a non-comformist youth culture based on Western values and fashion. Such cultural change from Stalin's dull era of Socialist Realism, again portrays a former method of control that developed into a way of undermining the state.