Monitoring integrity of a running computer system is based on creating a Test Model which includes predicates descriptive of invariant properties of security relevant objects and their attributes in the monitored structure known-to-be “healthy”, acquiring memory image of a portion of the running monitored structure, decomposing the acquired memory image to retrieve representation of the security relevant objects of interest, by implementing the attributes of the Test Model, and verifying, by implementing the predicates, whether the invariant properties defined in the Test Model remain unchanged for the running host system. If a discrepancy is detected, a signal indicative of a detected discrepancy is transmitted to a management entity for analysis and formulating a course of action.