scanlogd -- scanlogd is a TCP port scan detection tool
http://www.openwall.com/scanlogd/
scanlogd is a TCP port scan detection tool, originally designed to
illustrate various attacks an IDS developer has to deal with, for a
Phrack Magazine article, issue 53, article 1. Thus, unlike some of the
other port scan detection tools out there, scanlogd is designed to be
totally safe to use.