Environment

Adobe Mobile Marketing

Answer

Adobe’s Mobile App Libraries (available for iOS, Android, WP8) generate their own random unique visitor ID when an app is installed. This visitor ID is stored within iOS User defaults | Android - Shared preferences on the mobile device and is submitted as a “MID” value on each hit. 

A new visitor ID is generated if the user uninstalls and reinstalls the app (app visitor IDs persist through upgrades). If the User defaults or Shared preferences are deleted.

Additional resources