No it shouldn't be dangerous as iPV6 is the newest Internet communications protocol and your Internet Service Provider may be upgrading their service. Your ISP may be able to provide more information to you regarding what is happening there.
If you don't use a Network you can choose not to trust any networks and then you wont see any new popups.
Double-click the taskbar icon to open SecurityCenter
Click PC and Home Network Tools
Click Home Network Defense
That screen basically reflects what's showing in your Windows Network and Sharing Center
If you don't want to trust the network simply click on your router or modem in that screen and then click 'Don't Trust Network'
Or if you use a network you can identify whatever it is there and give it a name.
Have you connected any new devices either wirelessly or wired?
If not then you mark them as Intruders there and they will be blocked.
Your response helped me to find the attached link from Microsoft on IPV6 which is the transition from IPV4 allowing an unlimited number of IP address.