Port 80 in use by "Unable to open process" with PID 4!

[cbreemer]

Hi all, I'm new to XAMPP. Just installed version 8.1.2, and the one thing I needed to change was the port number, from 80 to 90, because IIS is already using port 80.
Now I am bemused by the Apache startup still giving an error about port 80 being in use, saying it will not start Apache, then proceed to start it and it works just fine on port 90 !

13:40:09 [main] Control Panel Ready
13:43:11 [Apache] Problem detected!
13:43:11 [Apache] Port 80 in use by "Unable to open process" with PID 4!
13:43:11 [Apache] Apache WILL NOT start without the configured ports free!
13:43:11 [Apache] You need to uninstall/disable/reconfigure the blocking application
13:43:11 [Apache] or reconfigure Apache and the Control Panel to listen on a different port
13:43:11 [Apache] Attempting to start Apache app...
13:43:11 [Apache] Status change detected: running

Not at all a problem, just wondering. I hate unexplained messages.