1. In combination with a data-processing system having at least one operating memory holding operating data, a protection unit comprising: an execution environment protected from unauthorized access; at least one monitoring logic in the execution environment connected to the operating memory for monitoring unauthorized modifications, access, or similar protection violations of the operating data stored in the operating memory and for generating an output on detection of such a protection violation; and a protection logic in the execution environment holding replacement data capable of replacing the operating data and connected to the monitoring logic for, on generation of the output, providing to the operating memory the replacement data for the operation or for a substitute operation of the data-processing system.