[mattmass]

Your point is completely valid. These aren't guaranteed to persist across all events, though OS installs should be ok if the user restores from a backup afterwards. The ability to delete/turn off is important, though. A tracking number that cannot be deleted and is shared across all applications is fundamentally at odds with user privacy.

SecureUDID does not claim to emulate a hardware ID. Uniqueness-per-app-only and ability to be disabled are its two defining features.