Mobile and Tablet UID

It is generally not recommended to use an identifier that is tied to the hardware of the device. If a user sells their phone to someone else, then the device ID does not change and you risk leaking information to another person. For this and other reasons, various platforms are deprecating and removing their device ID from the developer API. This is also problematic on Android 4.2 tablets with multiplayer support.

A lightweight approach, functionally equivalent but not leaking information in this way, is to generate a GUID the first time the application is launched, store it in user preferences, and use that GUID each time. This gives you a token that is unique to the installation of that device and app, saves a backup / restore if you wish, and still allows the user to erase data if they so choose. This has the added benefit of not requiring any exotic application rights.