A method to defend effectively against cold-boot attacks includes checking state data stored in a state memory to which the system software has access. At least two of the state data items are checked (111; 112) to determine deviations from parameters that are defined for a normal state of the computer. If deviations from the parameters are determined for at least two of the checked state data items, at least subareas of the main memory are cleared or overwritten (120); otherwise, the main memory is not cleared or overwritten (130); then, the system startup of the computer is carried out by means of the configured system software (140).