The Verge writes that Apple has apparently begun to crack down on apps submitted using the now deprecated UDID (unique device identifier) APIs that allow developers to track individual devices.
The programmer interface used to return an alphanumeric string unique to each deployed device. It was built out of a hash of the unit's serial number and other internal details. Apps that use the uniqueIdentifier API will automatically be rejected as this policy rolls out to its full complement of review teams.
Instead, developers are directed to create unique identifiers specific to applications. Those identifiers can then be stored securely in the device keychain and retrieved regardless of application uninstalls/reinstalls.
Although some developers have turned to using other approaches to track devices (for example, using the unit's MAC address), it's clear that Apple does not approve of any device-specific user tracking.
For now, in-store apps that use UDIDs do not seem in danger of being yanked. The policy seems to apply to all new and updated apps, however.
This may be the knell of doom for my Ad Hoc Helper app. Not sure where I'm going to go with that. If you have suggestions, drop a note or leave a comment.