[Shieh91] S. W. Shieh and V. D. Gligor, A Pattern-Oriented Intrusion-Detection Model and Its Applications, Proceedings of the 1991 IEEE Symposium on Research in Security and Privacy, page 327. [This paper describes a method for analyzing audit trails to detect known attack patterns based on previous information flow models. It is designed to operate in trusted systems where operational security procedures fail, but also has application to untrusted systems.]