> The 'filtered' ones are probably filtered by your ISP. I can understand (but > don't share) why they block port 25 or port 445) but I wonder why a ISP > would filter out port 80, aren't people allowed to have a web server at home?
I don't know if you remember the CodeRed and Nimba worms that were spreading like craxy, but ISPs decided to block 80 to slow down the spread and their customers. Most residential cable and dsl providers forbid customers from running servers. Most of the time, you will find in the terms of service, that they are not allowed. If you want to run a web or ftp server, they want you to go with a commercial service plan. While I've never heard of anyone getting their service cancelled because they ran a server on a residential plan, but you never know. Back to the orignal question, I would highly suggest setting up a basic firewall just to block the ports that aren't being used. The more granular you are the better.
