A computer network based digital information library system employing authentication and encryption protocols for the secure transfer of digital information library programs to a client computer system and a mobile digital information playback device removably connectable to the client computer system....http://www.google.co.uk/patents/US7765308?utm_source=gb-gplus-sharePatent US7765308 - Apparatus and method for authoring and maintaining a library of content and targeting content to a playback device
