BitTorrent is a widely used protocol for peer-to-peer (P2P) file sharing, including material which is often suspected to be infringing content. However, little systematic research has been undertaken to establish to measure the true extent of illegal file sharing. In this paper, we propose a new methodology for measuring the extent of infringing content. Our initial results indicate that at least 89.9% of files shared contain infringing content, with a replication study on another sample finding 97%. We discuss the limitations of the approach in this case study, including sampling biases, and outline proposals to further verify the results. The implications of the work vis - vis the management of piracy at the network level are discussed.