[AFMUG] how Windows determines "no Internet access"

[Ken Hohhof]

Googling for this, I find that Windows 7 supposedly goes to
http://www.msftncsi.com/ncsi.txt and wants to see the text Microsoft NCSI.
This seems plausible, does anyone know for sure?  And does Windows 10 do the
same?  Also, what triggers the captive portal detection?