You can go to grc.com to the "Shields Up" section and see what ports are open. I don't know if you are on a home network but I would make sure that if I were on windows "file sharing" was disabled and that I was updated with the latest security patches.
I am on a home network and use a NAT router and most of my ports would not show up on a port scanner. This capability is pretty much available on any hardware router. Additionally I have a software based router (Kerio). Zone Alarm, Tiny, Black Ice are a few others. This provides a second layer of protection. I would definetely do one or the other or BOTH if I had a broadband connection with a fixed IP.
Good Luck!
