The present invention relates to a computer system comprising: - multiple sets (S1, S2,...,Si,...,SI-1, SI) of client computers (Ci1, Ci2,...,Cij,...CiJ), each client computer having installed thereon an application program (104), the application program comprising client computer specific log-in information (Lij), - a database system (1,12) being coupled to the set of client computers via a network (114), the database system having a log-in component (118) for logging-in the client computers, the database system being partitioned into multiple relational databases (DB1, DB2,... DBi,...DBI), each one of the databases being assigned to one set of the sets of client computers, each database storing encrypted data items, each data item being encrypted with one of the user or user-group specific cryptographic keys, the key identifier of the cryptographic key with which one of the data items is encrypted being stored in the database as an attribute of the one of the encrypted data items, the log-in component comprising assignment information (118) indicative of the assignment of the databases to the set of client computers.
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