The invention is concerned with enabling substantially anonymous purchases of media products or other products (or access to an on-line service) to be made on-line. In order to initiate a purchasing session, consisting of one or more purchasing transactions, the purchaser authenticates himself to a home provider computer (3) which ten allots an anonymous client identifier (clientID) to the client for the purposes of that session. The purchaser (1) contacts a vendor computer (6), using the anonymous identifier (clientID) and an anonymising HTTP proxy, in order to place an order for one or more products or services for which the vendor computer has the right to authorize delivery. In order to obtain delivery of the product or service from the repository computer (5), the purchaser (1) provides the clientID to the repository computer (3).