When I tried to listen on port 80 in Windows 7 with netcat, I get this error:
C:\Users\sashoalm>echo "hello, world" | netcat.exe -l -p 80
Can't grab 0.0.0.0:80 with bind
On the other hand, selecting any other port works.
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sashoalm
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possible duplicate of http://superuser.com/questions/451348/how-to-know-which-port-is-busy-or-free-on-windows-7/451351#451351 OR [How to know who is listening to port 80 on Windows in multihomed case?](http://superuser.com/questions/726963/how-to-know-who-is-listening-to-port-80-on-windows-in-multihomed-case) OR http://superuser.com/questions/43307/why-is-system-process-listening-on-port-80 OR http://superuser.com/questions/246214/how-to-find-exe-listening-on-port OR http://superuser.com/questions/11207/how-can-i-see-all-active-connections – Dave Jun 20 '14 at 12:00
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It turned out this port was being used. I used netstat -a -b to find out which program uses it (it requires elevated privileges).
It turned out Skype will use port 80 and 443 for incoming connections, after reading https://support.skype.com/en/faq/FA148/which-ports-need-to-be-open-to-use-skype-for-windows-desktop, I changed that and now it works fine, netcat can listen on this port.
