Do you want to run a htttp daemon on ur computer but don't want millions of kids scanning it and trying to hack it (those evil hackers, damn them). This is a little useful trick to hide ur server:
I recently started running apache for a little personal site where I store stuff for me an some friends and I really hated the idea of having people finding my server and scanning it and trying out exploits on it etc. I did go through all the steps to secure it but I thought it would be better if I could hide it from view while still making it accessible to everybody. The answer was easy, change the port number apache (or any other webserver) listens on. And change it to a port that is not commonly used and won't be found in a port scan (there are 65535 ports, shouldn't be hard to find one that isn't used). Next, I would have to make it accesible for everyone, even if they don't know what port apache was running on. For the last part of the problem I remember the service SilentRage was using, sytes.net. I signed up for an account and had the http request redirected to my server like this "http://myip:11111" thats not the port I used but you get the idea. Now I ran an nmap scan and a nessus scan on my comp and neither of them showed that I have a webserver running, which would be enough to stop any script kiddie from trying to hack your website. Now of course somebody could scan every single port and find it that way but this will at least make ur little server a lot harder to find.