According to this article carried on PC World, NSA hitchhiked on Google’s cookie to select specific target to snoop. This article also shows you how to check the cookies on your computer. If you are interested, you can follow the steps. Basically, it is:
1. Go to Google.com
2. Right click and choose inspect elements
3. On the lower portion of the screen, click on Resources tab and you will see your PREF cookies.
4. Notice the ID. That is unique to your browser and that is how Google spy on you. Now NSA simply takes a free ride on that and can spy on you, too, if they want to.