Blocking an unknown device?

[Afrelich]

This morning I had a notification that a new device had connected to my network. It was classified as a router, called Technicolor CGM4140COM. I do not recognize the device and paused it immediately- there did not appear to be any activity- but could not see how to block it, other than forgetting the device, which would allow it to reconnect. Any suggestions?

[EG]

Their Advanced Security feature has recently been pushed to their gateway devices via a firmware update whether you want it or not, hence the hypochondriac notices. It's buggy.

We've seen many many posts about this here lately ! The work-around is to disable the Advanced Security and not use it for now, it's buggy.;

https://www.xfinity.com/support/articles/using-xfinity-xfi-advanced-security