<FONT face=Verdana>The existing methods for misuse detection of information systems are restricted because of their own limitations

such as unable to detect new kinds of misuse and need the knowledge of potential misuses. A hidden Markov model (HMM) based method is presented to detect the misuse of resource in information systems. In the HMM model

the file folders containing sensitive information are taken as the model states and the user operations as the model observation symbols. Baum-Welch algorithm is adopted to determine the model parameters. The behavioristic profiles of the insiders are determined by the HMM model and used to detect malicious actions. The simulation results show the effectiveness and adaptability of our method.