net/snort 2.9.20p7 OpenBSD

Snort is an open source network intrusion detection and prevention system. It is capable of performing real-time traffic analysis, alerting, blocking and packet logging on IP networks. It utilizes a combination of protocol analysis and pattern matching in order to detect a anomalies, misuse and attacks. Snort uses a flexible rules language to describe activity that can be considered malicious or anomalous as well as an analysis engine that incorporates a modular plugin architecture. Snort is capable of detecting and responding in real-time, sending alerts, performing session sniping, logging packets, or dropping sessions/packets when deployed in-line.

Snort has three primary functional modes. It can be used as a packet sniffer like tcpdump(8), a packet logger (useful for network traffic debugging, etc), or as a full blown network intrusion detection and prevention system.