"For more than eighty years, Dutch security services perceived communism as the ultimate threat to national security. From its inception, the anticommunist threat perceptions contained references to foreign, possible, potential, and ideological elements of the communist threat. This put the activities of Dutch communists in a different light. Although for a long time there were well-grounded reasons to do so, the author finds that there were periods when the actual threatening character of Dutch communism decreased. However, the security services did not decrease their surveillance activities vis-a-vis this 'red menace'. To account for this discrepancy, he uses insights from securitization theory, organizational studies, and intelligence studies to deconstruct threat perceptions. The author finds that whenever actually threatening events, such as the revolutionary threat of 1918 or the World Wars, became part of a distant Aast, the security services emphasized the symbolic and potential nature of the communist threat. The symbolic character of the threat institutionalized and continually reinforced by processes of cognitive bias, thus accounted for its unchanging threatening character. Only through external intervention have these perceptions changed." (author's abstract)