This network intrusion detection and prevention system excels at traffic analysis and packet logging on IP networks. Through protocol analysis, content searching, and various pre-processors, Snort detects thousands of worms, vulnerability exploit attempts, port scans, and other suspicious behavior. Snort uses a flexible rule-based language to describe traffic that it should collect or pass, and a modular detection engine. Also check out the free Basic Analysis and Security Engine (BASE), a web interface for analyzing Snort alerts. While Snort itself is free and open source, parent company SourceFire offers their VRT-certified rules for $499 per sensor per year and a complementary product line of software and appliances with more enterprise-level features. Sourcefire also offers a free 30-day delayed feed.
Snort® is an open source network intrusion prevention and detection system (IDS/IPS) developed by Sourcefire. Combining the benefits of signature, protocol, and anomaly-based inspection, Snort is the most widely deployed IDS/IPS technology worldwide. With millions of downloads and nearly 400,000 registered users, Snort has become the de facto standard for IPS.
We strongly recommend that you keep pace with the latest production release. Snort is evolving all the time and to stay current with latest detection capabilities you should always have both your Snort engine and ruleset up to date.