snort-doc 2.8.5.2-5 (amd64 binary) in ubuntu natty

 Snort is a libpcap-based packet sniffer/logger which can be used as a
 lightweight network intrusion detection system. It features rules
 based logging and can perform content searching/matching in addition
 to being used to detect a variety of other attacks and probes, such
 as buffer overflows, stealth port scans, CGI attacks, SMB probes, and
 much more. Snort has a real-time alerting capability, with alerts being
 sent to syslog, a separate "alert" file, or even to a Windows computer
 via Samba.