Security safeguards provided by the operating system software include access controls, user identification, memory bounds control, etc. As a result of a hardware malfunction, especially a transient one, such controls can become inoperative. Thus, internal checks are necessary to insure that the protection is operative. Even when this is done, the simultaneous failure of both the protection feature and its check mechanism must always be regarded as a possibility. With proper design and awareness of the risk, it appears possible to reduce the probability of undetected failure of software safeguards to an acceptable level.
How often should systems be reviewed / updated?