1. A system for network content monitoring, comprising: at least one processor and an electronically readable medium, a transport data monitor, connectable to a point in a network, for monitoring data being transported past said point, a description extractor, associated with said transport data monitor, for extracting descriptions of said data being transported, a database of at least one preobtained description of content whose movements it is desired to monitor, a comparator for determining whether said extracted description corresponds to any of said at least one preobtained descriptions, thereby to determine whether said data being transported comprises any of said content whose movements it is desired to monitor, and certification recognition functionality to recognize data sources as being trustworthy and to allow data transport originating from said trustworthy data sources to pass through without monitoring.