The invention relates to a system and method for operating a billing system associated with a mobile radio network for billing for tariff based use of data provided by a network-external data store, where the data are used by virtue of their being retrieved using a mobile terminal belonging to a user of the mobile radio network, and to a data transmission network. The mobile terminal transmits a user address identifying the user to an intermediate node connected to the mobile radio network, the intermediate node generates an anonymous user identifier from the user address using an encryption method and transmits it to the data store. The data store transmits a cost variable, associated with the retrieved data, and the anonymous user identifier to the billing system, and the billing system recovers the user address and debits a cost account which is associated with the user.