It is known that BitTorrent file-sharing traffic is analysed to identify exchangers of copyrighted material. In general, copyright holders can perform monitoring using two approaches:
, where indirect clues of the sharing activity of a peer are considered (e.g., its presence in the peer list of a tracker), and
, which establishes connections with peers to estimate their participation in sharing activity. Previous research has focused exclusively on indirect monitoring. We provide a broader characterisation of the monitoring of BitTorrent activity by considering both indirect and direct monitoring. In particular, we review previous work on indirect monitoring, provide features to detect peers engaged in such monitoring, and apply them to identify a number of monitoring organisations. Additionally, we introduce features that detect direct monitors, and provide the first ever measurements of direct monitoring, showing that it is now occurring.