Abstract: Systems and methods are provided for persistent cross-application mobile device identification. A mobile device may have a plurality of sandboxes in memory containing applications. The mobile device may have a shared storage which may accessible by applications from different sandboxes. A storage location identifier may be used to access information in shared storage. A universal device identifier may be stored in the shared storage to identify the mobile device and may be accessible by multiple applications and updates to applications. The universal device identifier may be used to track the mobile device for advertising, fraud detection, reputation tracking, or other purposes.