Question : How does Windows 7 detect Internet access?

I noticed a new feature in Windows 7 where it detects if you are connected to a network and then goes out to try to determine if you are connected to the Internet. Can anyone explain to me what kind of check it runs to determine if you have Internet access or not? I am not having any issues with this functionality, I am simply curious about how it works and searching Google hasn't revealed anything other than people having issues.

Answer : How does Windows 7 detect Internet access?

1. triest to nslookup dns.msftncsi.com (131.107.255.255)
2. tries to download ncsi.txt  from msftncsi.com. It should contain "Microsoft NCSI".