Even if you do ultimately perform the clean install of Windows, removing whatever that device is, I'd still install Glasswire afterwards, just in case. It will be able to tell you exactly how much data your PC is using, and just what is using it (program, app, device, process, etc.). It's a really handy tool, especially for being free. Unfortunately, it only monitors the data usage for the device on which it's installed rather than all devices on your home network, but it can still be a very useful and helpful tool. If you do perform the clean install, don't forget to save any important data before doing so. It would also be a good idea to have at least the WiFi driver on hand in case it needs to be installed after the Windows install. This way you'll be able to connect to the net in order to get any other drivers the system may be missing. I would normally recommend saving all of the drivers on the system, but with it currently having an unknown and possibly nefarious one, I wouldn't do so. And if you don't know the Windows Product key, I'd try to glean that from the system as well, just in case. I can usually find it using the Command Prompt method outlined here (I collect mini PCs and do this with all of them).
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