Mobile Device IDs : If you're using an app, we use mobile device IDs (the unique identifier assigned to a device by the manufacturer), instead of cookies, to recognize you. We do this to store your preferences and track your use of our apps. Unlike cookies, device IDs cannot be deleted. Ad companies use device IDs to track your use of the app, track the number of ads displayed, measure ad performance and display ads that are more relevant to you. Analytics companies use device IDs to track information about app usage. 