SecureUDID is an open-source sandboxed device identifier solution aimed at solving the main privacy issues that caused Apple to deprecate UDIDs.
SecureUDIDs have the following attributes:
Developers can still differentiate between devices as if they were still using a UDID, but only within apps they control.
User privacy is protected since developers are fundamentally prevented from accessing the same UDID as another developer. This greatly limits the scope of any potential leaks.
End-users can globally opt-out of SecureUDID collection across all applications and services that use it.