ShieldsUp web based port scanner can test the security of your firewall right from the webpage that it lives on. Shields up is very easy to use and can test the security of your firewall and list the open ports at the push of a button. This tool can also be used to test for messenger spam, and browser headers
ShieldsUp can also be very useful when you don’t have the password to the router of the network that you’re working on and you need to see what ports are open on the firewall.
There are also many other great freeware security test applications available at the Shieldsup website at GRC.com.