A method and an apparatus are provided for detecting peer-to-peer communication on a data communication network, between an internal client machine within an internal address space and an external client machine. The method includes routing all messages addressed to internal client machines to an analysis device. The analysis device identifies messages pertaining to peer-to-peer communication andidentifies the internal client machine to which the messages of a specified nature were addressed. The analysis device terminates the connection with the external client machine if the establishing of the peer-to-peer communication is in violation of a pre-determined internal network rule.