When someone tries to a blacklisted port, I'd like that IP address to be blocked at the firewall, for everything. Even port 80. Essentially I have a webserver, and see folks walking through ports to see what's available. Obviously, they're up to no good and I'd like to slam the door on them. Is there a script that can do this? Even if it's cron based, that's fine...
You're probably looking for psad.
And here is a great tutorial on Detecting And Blocking Port Scan Attacks In Real Time.