A method and computer system are provided for distributing a plurality of data portions from a server system to one or more client systems. The method includes receiving one or more first requests at the server, each first request being submitted by a client system and including a portion identifier, wherein a portion identifier is assigned to each data portion; in response to receiving the first request(s), transmitting a list of chunk identifiers to the requesting client systems, wherein the list of chunk identifiers specifies the data chunks whose meta-data includes the portion identifier contained in the first request; and transmitting some or all data chunks of a data chunk library to each of the requesting client systems. At the requesting client system, the client specifically selects the data chunks of the transmitted data chunks which are specified by the received list of chunk identifiers.