Each time you visit a page on the Internet its a good change that a service on that page is tracking you. Below is a listing of some of the common ways a web page will track you when its being viewed. To view how a website is tracking you, block services, and get a better understanding about each tracking services install Ghostery, a free tool that displays all tracking services and gives you additional details about each service. In the picture to the right, is an example of a Ghostery window being displayed for the CNN website, in this example this page normally has eight services tracking the visit, however, six of the services have been disabled.

How a website may track you

• Most sites collect analytical data using services such as Google Analytics to help the owner of a website understand how their web page is being used.
• Sites with share buttons from Facebook, Google+, and other social networks will also track each visitor that views the share button or a social network plugin. Users logged into these social services can be tracked and also share the pages through the services.
• Many advertisers such as Google (DoubleClick) will track where their advertisement banners are displayed.
• Hundreds of other services that monitor traffic, brands, patterns, mobile, etc. for research and advertisers.

http://www.ghostery.com/