This week we spotted the new system, "Advertising ID," in the wild. We know it's being used to track users with newer versions of Android phones. We believe it is running on KitKat, the latest version of Android. Below, we'll show you how to locate Advertising ID in your settings and turn it off or on.
What we don't know is exactly how it works, or what it is tracking. But given that it's intended to provide usage data for advertisers, it's a reasonable assumption that it's tracking your web browsing and possibly your app usage too. One possible difference is that Advertising ID may be tracking your phone specifically, whereas cookies track your behavior. Here are its terms of service for app developers.