Computer security is a topic of growing concern because, on the one hand, the power of computers continues to increase at exponential speed and all computers are virtually connected to each other and because, on the other hand, the lack of reliability of software systems may cause dramatic and unrecoverable damage to computer systems and hence to the newly emerging computerized society. Among the possible approaches to improve the current situation, expert systems have been advocated to be an important one. Typical tasks that such expert systems attempt to achieve include finding system vulnerabilities and detecting malicious behaviour of users. We extend our intrusion detection system ASAX with a deductive subsystem that allows us to assess the security level of a software configuration on a real time basis. By coupling the two subsystems-intrusion detection and configuration analysis-we moreover achieve a better tuning of the intrusion detection since the system has only to enable intrusion detection rules that are specifically required by the current state of the configuration. We also report some preliminary performance measurements, which suggest that our approach can be practical in real life contexts.

An implemented system for on-line analysis of multiple distributed data streams is presented. The system is conceptually universal since it does not rely on any particular platform feature and uses format adaptors to translate data streams into its own standard format. The system is as powerful as possible (from a theoretical standpoint) but still efficient enough for on-line analysis thanks to its novel rule-based language (RUSSEL) which is specifically designed for efficient processing of sequential unstructured data streams. The generic concepts are applied to security audit trail analysis. The resulting system provides powerful network security monitoring and sophisticated tools for intrusion/anomaly detection. The rule-based and command languages are described as well as the distributed architecture and the implementation. Performance measurements are reported, showing the effectiveness of the approach.>