Si to vypni tu kontrolu:
HKEY_LOCAL_MACHINESYSTEMCurrentControlSetServicesNlaSvcParametersInternet
Under the Internet key, double-click EnableActiveProbing, and then in Value data, type: 0.The default for this value is 1. Setting the value to 0 prevents NCSI from connecting to a site on the Internet during checks for connectivity.
V té větvi registru vidíš, kam to leze a co to kontroluje. Asyk to máš bloknuté..?

Jinak to kontroluje, zda existuje soubor connecttest.txt

Windows 10 or later versions:
NCSI sends a DNS request to resolve the address of the www.msftconnecttest.com FQDN.
If NCSI receives a valid response from a DNS server, NCSI sends a plain HTTP GET request to http://www.msftconnecttest.com/connecttest.txt.
If NCSI successfully downloads the text file, it makes sure that the file contains Microsoft Connect Test.

NCSI sends another DNS request to resolve the address of the dns.msftncsi.com FQDN.
If any of these requests fails, the network alert appears in the Task Bar (as described in Symptoms). If you hover over the icon, you see a message such as "No connectivity" or "Limited Internet access" (depending on which requests failed).
If all of these requests succeed, the Task Bar shows the usual network icon. If you hover over the icon, you see a message such as "Internet access."