A method of protecting a microcomputer system against manipulation of data stored in a storage assembly of the microcomputer system, in particular a control program stored there. Checking mechanisms are executed at preselectable points in times to check for manipulation of the data. To achieve the most complete test coverage within an acceptable period of time in checking data stored in a storage assembly of a microcomputer system, the storage assembly is subdivided into multiple logic blocks, at least one of the blocks is selected and the checking mechanisms are executed only for the or each selected block of the storage assembly.