Abstract: A system for controlling data access in a computer network comprises first means for establishing a first communication link between a client computer and a server computer. The client sends a request to the server for supply of a data item from the server to the client. The server selects the requested data item from a store of data items in response to the request from the client. The server associates each data item in the store with a service telephone number. The server also identifies a subscriber telephone number associated with the request. A second communication link is then established between the server and a telephone utility. The server instructs the telephone utility to register a telephone call from the subscriber telephone number to the service telephone number associated with the requested data item. The requested data item is supplied from the server to the client on receipt by the server of confirmation from the telephone utility that the telephone call is registered.