If someone was able to initiate a connection to your desktop behind a router, and you did not manually set up port forwarding, it sounds like you have UPnP enab

If someone was able to initiate a connection to your desktop behind a router, and you did not manually set up port forwarding, it sounds like you have UPnP enabled. I strongly suggest turning that off. This would not happen behind any home router I know of with UPnP disabled, unless you have malware on the machine.