Windows 10: what is the Best way to protect my computer from intruders

What is the best way to protect my computer from intruders

:)

 

Intruder? Connecting to my wi-fi and saying that it's me

I have found something concerning, especially since I work from home.

My net has been unstable the past few days and I decided to check how many users are connected to my Wi-Fi. I found 2 devices that share the same "name", and initially, the wrong one was marked as "my computer". After checking the local IP address, I found
that the other device was in fact my computer.

I disconnected the Wi-Fi entirely (ethernet connection only), I turned off every mobile device and unplugged every device that required an ethernet connection; I disconnected everything except for my main computer connected with a cable, but the intruder
was still showing up on the list.

I would have thought that both devices are my own computer, but that's not the case: The intruder is connecting and disconnecting from my router as it pleases. 42 times I refreshed the list since Saturday night, and 42 times my PC showed up. The intruder
showed up 31 times.

As an odd detail: Yesterday night, I checked the list at 9:00 PM and the intruder was not there. At 9:50 PM my net was unstable and it disconnected itself, so I checked the list again as soon as the net was back, and the intruder showed up.

The only conclusion that I have from all this is that a program (or a virus) within my PC is getting activated from time to time, and when it does, it makes my net connection to go off and on. I ran my Antivirus (Avast) and no malware was found.

I'm seriously getting paranoid here since I ran out of options. Anyone that could share any suggestions about this? How can I identify that program, or that device? I also blocked the MAC address from my router but it keeps showing up.

 

Clear Windows Security Center (Defender) Protection History

Did not work for me. After going through all steps I still have protection history full

 

System Protection Recovery

Windows 10

1. Step 1: Right-click the lower-left corner and open System in the Quick Access Menu.
2. Step 2: Choose System protection on the left.
3. Step 3: Select a hard disk and tap Configure to move on.
4. Step 4: Choose Turn on system protection and hit OK.
5. Step 3: Select Disable system protection and hit OK.