Abstract: A file transfer method is disclosed in which in which a client (100) requests a file from a server (110) and the server (110) sends to the client (100) one or more data segments which data segments together constitute content of the requested file and additional content provided by a service provider. A benefit that may be provided by at least preferred embodiments is that a provider of download files, and in particular audio files, may add additional material such as advertising material to the download content. Targeting of the material to a particular user might be achieved by asking the user to provide information about their interests, and selecting for inclusion those advertisements that most closely accord with the user's a preferences. To reduce storage requirements, the server may store a virtual file reference for each user and construct a customised file dynamically.