Today, at work, someone took control of my desktop(Windows PC). The intruder was clicking around as if they can see my icons, menus etc.

I am connected to the LAN at work. So I yanked out the cable and also disabled the WIFI adapter. So from the network connection point of view there were NO connections. Lastly the only peripheral I had is a mouse that uses a WIFI dongle.
I disconnected the dongle and the activity stopped.

This evening I will be killing my mouse and dongle with fire - I no longer trust it.

I am not a noob when it comes to IT but this I must admit was intriguing and unnerving.

Any help / clarity would be great.