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 matchingin 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(1), a packet logger (useful for network traffic debugging, etc), or as a full blown network intrusion detection and prevention system.