Building intrusion detection model in an automatic and online way is worth discussing for timely detecting new attacks. This paper gives a scheme to automatically construct snort rules based on data captured by honeypots on line. Since traffic data to honeypots represent abnormal activities, activity patterns extracted from those data can be used as attack signatures. Packets captured by honeypots are unwelcome, but it appears unnecessary to translate each of them into a signature to use entire

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... payload as activity pattern. In this paper, we present a way based on system specifications of honeypots. It can reflect seriousness level of captured packets. Relying on discussed system specifications, only critical packets are chosen to generate signatures and discriminating values are extracted from packet payload as activity patterns. After formalizing packet structure and syntax of snort rule, we design an algorithm to generate snort rules immediately once it meets critical packets.