I just moved and got a new modem/router from Xfinity. Changed SSIDs and changed passwords for WiFi. I have one desktop connected to Ethernet. I've had this for a week now. The only thing I have done is changed the Ethernet cable because it was ripped up. When I logged into my gateway last night I saw a random MAC address under the "Offline Devices" with only a IPv6 address that said it was connected previously through Ethernet and not WiFi. Should I be concerned??