The aim of Ghost Port Scan is to provide administrators and pen-testers
with a tool that allow them to easily test firewalls and get information
from a remote host.

GPS is a port scanner and a firewall rules disclosure (FWRD) tool, which
uses IP spoofing, ARP poisoning and some other stratagems in order to
perform a stealth and untrackable information collect.

As far as GPS needs to sniff the responses from the target host, it
requires to be run using a loopback or an ethernet interface (including
cable modem).

WWW: http://gps.sourceforge.net/