We propose a mechanism for the acquisition of information from potentially unreliable sources. Our mechanism addresses the case where the acquired information cannot be verified. The idea is to intersperse questions (“challenges”) for which the correct answers are known. By evaluating the answers to these challenges, probabilistic conclusions about the correctness of the unverifiable information can be drawn. Less challenges need to be used if an information provider has shown to be trustworthy. Our approach can resist collusion and shows great promise for various application scenarios such as grid-computing or peer-to-peer networks.