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For many intelligence and security applications it is important to know how close people in a network are. In online social networks (OSN) friendship links are a frequently chosen basis for the analysis. In this paper we show that friendship links can be misleading, if we want to know to what extent people in a network trust into each other. We also show how to unveil hidden friendship relations based on an analysis of exceptions in the privacy settings. We furthermore discuss resulting options for defeating crime and terrorism as well as associated privacy, security and civil liberty issues.