A method for tracking digital files transmitted over the Internet by placing certain identifying indicia within a file, and monitoring selected sites through which Internet traffic is transmitted, to determine the source and destination of a transmission containing a file with particular identifying indicia. Identifying indicia (`ID`) is placed in the header of each digital file whose transmission over the Internet is to be monitored. A data communications monitoring device is installed at a Internet service provider's (ISP's) facility. The monitoring device intercepts packets received by the ISP. These intercepted packets are then examined to determine whether they contain an ID of interest. If a sought ID is found within the packet, the source and destination fields in the Internet Protocol (IP) header are logged, along with the ID and other information, in a database. The pertinent contents of the database are then periodically sent to the proprietors whose IDs were discovered in packets in transit across the Internet. A proprietor may then take appropriate steps to secure compensation for the unauthorized copies, or to prevent further dissemination thereof.