Just realized

Since I installed Ubuntu 9.04, I haven't tested my firewall at "Shields Up".You have probably heard about it or even used it! If not, it's quite simple to use. Just go to the above link, let the page load. It will tell you who your isp is. just go down the page a little, you will see a "proceed" button. Click it! Another page loads with some info etc, and you will notice a row of grey buttons. The middle button is what we are looking for, it says "All Service Ports". Click that then sit back and watch your computer being probed! We are aiming for all green ports, that means stealth mode, no one can see you on the internet.If you get blue, this means your ports are blocked but you can be seen. If you get red your ports are open! You don't want that!

Shields up also pings your computer, to see if it responds (which we don't want either). When the test is finished, you will see the findings at the bottom. By the way, if you put the cursor on a coloured block, it will tell you which port that is, if you click one it will give you even more info.