New Arris device connected to my Xfinit network

@user_ygwm1v, thank you for using the Community Forum, we know how important network security is. Have you had a change to check all the connected devices to your network and name them in order to know what each one is? 

Recommendations?  https://forums.xfinity.com/conversations/your-home-network/unauthorized-users-moca/6565e1dc93c02b495090a92d?commentId=6565ef8c1863db460fe80749 

It's likely your neighbors Arris coax connected cable TV box if you are in a close neighbor situation (apartment/townhouse).  Their devices may join your network via MoCA if you use Xfinity equipment (Ethernet over coax).  This is a long running security problem.  You are exposed to your neighbors illegal internet use -- possible legal problems, privacy violations, data theft, maulware and viruses from their network, running up your data use, it's a mess. 

Xfinity pretends not to know what it is, but the reality is they don't want to have to isolate every cable install with an MoCA Point of Entry Filter to block your MoCA signal from leaking out, or from your neighbors devices getting in.  You can fix this yourself.