SNORT

SNORT is an open source suite of network security tools. It comprises a Network Intrusion Prevention System (NIPS) and a Network Intrusion Detection System (NIDS). The suite can perform realtime traffic analysis and packet logging on IP networks. It performs protocol analysis to detect threats as well as content searching and matching. In addition to the realtime analysis the suite can detect attacks and probes against networks. For example OS fingerprinting attempts, buffer overflows, stealth port scans CGI attacks, and Server Message Block (SMB) probes.