A system in which data signatures are used to identify copyrighted content passing through a network. The data signatures are derived from files containing copyrighted content to be identified. The signatures are used to search within peer-to-peer data streams flowing through one or more network nodes in a communications network. Any specific technique may be used for pattern recognition between the signatures and the monitored traffic. When a particular file of interest is identified, the system may operate to perform one or more of several possible actions, including stopping the transmission, allowing the transmission but recording the event, making an offer to the recipient allowing them to legally purchase the file, or sending alternative information or intentionally corrupting the information to render it useless to the recipient.