A system for network content monitoring and control, comprising: a transport data monitor, connectable to a point in a network, for monitoring data being transported past said point, a signature extractor, associated with said transport data monitor, for extracting a derivation of said data, said derivation being indicative of content of said payload, a database of preobtained signatures of content whose movements it is desired to monitor, and a comparator for comparing said derivation with said preobtained signatures, thereby to determine whether said payload comprises any of said content whose movements it is desired to monitor. The monitoring result may be used in bandwidth control on the network to restrict transport of the content it is desired to control.