How could Google Latitude find my exact PC location with no GPS or public WiFi?

Solution 1:

When Google made pictures for "Street View" they also collected data about available wireless networks. Cellphones with the Android operating systems can use this data to determine their location via "Assisted GPS" (faster than traditional standalone GPS) and they also transmit information about available wireless networks back to Google.

Although you have hidden your SSID (="Wi-Fi name"), each Wi-Fi-router has a globally unique "hardware address" called the MAC address. MAC means Media Access Controller and is not related to Apple's "Mac" trademark. Each piece of information sent from/to your router contains the sender's and the receiver's MAC address.

How Google finds you even without GPS:
"Google is trying to locate you" means: "Do you want to tell Google that you are connected to a wireless network with the MAC 10:9a:dd:2b:49:4d and that there is another wifi device nearby with the MAC 10:9a:dd:3b:3d:5f?"

If Google knows where one of the two devices is, then it knows where you are.

Solution 2:

First, just because your SSID is not broadcasting, that does not mean you are not emitting radio transmitter waves. That said, they do not seem to use that when you are doing it from a browser. Here is the exact explanation of how they do it when you use a browser:

http://en.wikipedia.org/wiki/W3C_Geolocation_API

Of course, when installed on a phone, I believe every phone today comes with a locator.