A computer system connected to a data communications network, wherein the computer system is reliably protected against computer viruses, unauthorized access to internal data, and loss of data in the event of infection with computer viruses. The computer system has a first computer (1) and a second computer (2) that is independent of and redundant to the first computer. The two computers match themselves by comparing their work results. The receipt of data from the data communications network (6) is limited to the first computer, and the transmission of data to the data communications network is limited to the second computer. At least the initial processing of received data is limited to the first computer, and non-verified or non-verifiable data received by the first computer are stored in the second computer only in locked form, i.e., in non-processable form.