Abstract: Controlled access to digital works using a network employs a dynamically updated client identification code to uniquely identify the client to a server, a content identification code to identify digital work, and a client software module as an agent of the server. An encrypted secret or unencrypted authorization code allowing access to the data content is transmitted to the client. Transmitting an encrypted secret to the client over an insecure communications network supports encryption of the digital work. A database association provides for a software license environment for copies of different digital works and at least one machine. Distributing supplemental data content (e.g. advertising) from one or many servers to a client involves contacting an authentication server to determine whether access to the primary digital work should be provided to the client, retrieving from a data content server the supplemental data content and transmitting the supplemental data content to the client for display.