I was looking around on Slashdot tonight and found the article “Windows 7 Network Awareness: How Windows knows it has an internet connection“.
The question that the article answers is:
Whenever I connect to a WiFi network which requires in-browser authentication, such as university networks and hotel access points, Windows somehow magically knows. Windows also knows when your internet connection isn’t working, and can differentiate between having local LAN access, no network access at all, or full internet access. But how?
The technique Windows uses is described.
Evidently it means that Microsoft always knows and logs your IP address, at least on public networks.
1. NCSI performs a DNS lookup on http://www.msftncsi.com/ncsi.txt, then requests http://www.msftncsi.com/ncsi.txt. This file is a plain-text file and contains only the text Microsoft NCSI.
2. NCSI sends a DNS lookup request for dns.msftncsi.com. This DNS address should resolve to 126.96.36.199. If the address does not match, then it is assumed that the internet connection is not functioning correctly.
I wanted to make sure to keep the code to turn on/off this functionality.
From the article:
2. 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.
I know I’m going to want to be able to control this functionality some day.