A method is for activating or deactivating at least one part of data stored in a memory arrangement of a microcomputer system, in particular one part of a program stored there. In the event of a manipulation of data stored in the memory arrangement by unauthorized third parties, a method having the following method steps may prevent utilization of the manipulated data reliably and effectively: a microcomputer-individual identifier is stored in a signed or encoded fashion a specifiable memory area of the memory arrangement; when the microcomputer system is started up, the signature of the identifier is checked or the identifier is decoded; and as a function of the result of the identifier, one part of the data is activated or deactivated.