Skype listens on port 80!
Last night, I was sitting down to do some casual work on my laptop while watching TV with my wife, when I encountered an interesting problem. I needed to setup a new virtual directory in IIS for the stuff I was working with, and when I opened the IIS admin tool, the Default Web Site was being shown as stopped. I scratched my head and went to try to start it, and it failed. Interesting. I hadn't really changed anything on my laptop in a while, and it was working fine not too long ago.
So, I open up the Windows event log and find an entry for it that says it failed to started because something else was bound to port 80. At this point, I flip out. Nothing else should be using port 80. I figured I had some sort of malicious spyware on my system that allowed a backdoor through port 80.
I immediately disable the wireless card to cut off all network access. Then I open up a command prompt and run 'netstat -b' and find out that oddly enough, Skype is bound to port 80. I scratch my head like, why the heck is Skype using port 80? I exit Skype, go back to IIS, try to restart the site, and it loads just fine. Ok. Now why?
I re-open Skype and proceed to look through its settings and find that it has an option for "Use port 80 and 443 as alternatives for incoming connections". Ok, now it makes sense. But then I look at my desktop and it has the same setting enabled, but yet I've never had a problem with Skype using port 80 on my desktop. Both Windows XP Pro SP2, but never happened on my desktop. I had just installed Skype on my laptop last weekend, so that is why it was happening just recently on the laptop, but still, I didn't understand why my laptop and not my desktop. They don't have the same port setting for inbound connections, to there isn't an issue with the firewall. So I don't know.
So to other developers out there (or just regular Skype users), beware of Skype taking over your port 80!