Bro is the only other real open source network intrusion detection system supported by a significant community of users. Vern Paxson of the University of California at Berkeley is the lead developer. Bro is considered a specification-based network IDS. Bro uses a variety of protocol analysis modules to inspect traffic and make judgments regarding its conformance to various norms. It is actually a very powerful complement to Snort.
This was first published in January 2008