If I understand you correctly then this has nothing to do with adblocking.
Well, it is more I guess a question about how to use IPTABLES than anything else... That is why it was placed here in this thread. Now as you might have read, it seems to be misplaced due to that the firewall should do exactly what I am asking for. While I might nog be 100% convinced yet about port scanning "people", the general idea is of course correct with the firewall.
All scripts, be it adblock, blocking countries from accessing open ports or the script (somewhere on this forum, can not find it for the moment) that blocks IPs from scanning ports in the future, will be using some sort of IPTABLEs.