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.

Note that --libdir seems to be ignored on Slackware64; libraries are installed
to /usr/lib anyway.