BitThief is freely available. We encourage you to download and use it. As it is a scientific project, we require measurements of the performance of our exploits. For that purpose, the client occasionally transmits data to our webserver. The transmitted data merely contains information about the time required to download files of different size. In particular, only a hash of the info hash is transmitted, which means that it is not feasible to determine what has actually been downloaded. However, we advise you not to download any copyrighted material.