There are some tools to check who is portscanning your machine and
when. A good tool seems to be ippl, the IP Protocols Logger,
but others include snort and portsentry.
In kernel 2.4 iptables has a mechanism for portscans where you can set
it up so that most portscans will take hours to return nothing.
Copyright © 1995-2006 Graham.Williams@togaware.com