The invention relates to methods for storing and finding data of clients which are identifiable by unique client identifiers on a memory device, wherein these data include at least client data identification values which the client assigns arbitrarily to the data, and these data of the client are found on the memory device exclusively by means of these client data identification values. An access control entity is provided which has an adaptable positive list as a listing of the client identifiers of the selected client which, exclusively in a session setup step, beginning with a session start enquiry, obtain a temporary supplementary information item from this access control entity and with this information item can store and find data on the memory device, each temporary supplementary information item losing its validity after a specific time period.