iOS6 UDID - What advantages does identifierForVendor have over identifierForAdvertising?

Question

Apple is changing their privacy settings for iOS6 and deprecating device UUIDs (UDIDs). According to a WWDC presentation and the docs there are two replacements for the UDIDs, both in the UIDevice class:

-identifierForVendor

• ID that is identical between apps from the same developer.
• Erased with removal of the last app for that Team ID.
• Backed up.

-identifierForAdvertising

• Unique to the device.
• Available to all applications; used for advertising — iAd has converted from UDID for iOS 6 and later.
• Reset with "Erase All Content & Settings".
• Backed up.

It seems to me that -identifierForVendor is inferior to -identifierForAdvertising since it would get reset on last uninstall of an app from a vendor and by "erase all contents & settings".

What advantages does -identifierForVendor have over -identifierForAdvertising?

Answer 1

Important Note:

Apple just released iOS 6.0 and the NDA has been lifted.

For developers who preemptively included code that referenced

[[UIDevice currentDevice] identifierForAdvertising] 

this method has NOT been included on iOS 6. If you use the above method, your app will (most likely) crash and be rejected!

Instead, Apple has created a new class ASIdentifierManager , which includes the method advertisingIdentifier. Here's the apple docs on it:

Answer 2

Users can limit the use of ad tracking on their phone. See this article on the opt-out mechanism under Settings > General > About > Advertising.

The new ASIdentifierManager class has a property advertisingTrackingEnabled, which returns true or false depending if the user has limited ad tracking. Even though the device's advertising identifier is returned by the advertisingIdentifier property regardless of opt-out, you aren't supposed to use the identifier if the user has opted-out.

So the advantage of identifierForVendor is that you'll always have access to and the right to use this id for the phone regardless of user's opt-in or opt-out for advertising tracking.