A document accessible over a network can be registered. A registered document, and the content contained therein, cannot be transmitted undetected over and off of the network. In one embodiment, a plurality of stored signatures are maintained in a signature database, each signature being associated with one of a plurality of registered documents. In one embodiment, the signature database is maintained by de-registering documents by removing the signatures associated with de-registered documents. In one embodiment, the database is maintained by removing redundant and high detection rate signatures. In one embodiment, the signature database is maintained by removing signatures based on the source text used to generate the signature.