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 an 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.