Starting May 1, the App Store will no longer accept new apps or app updates that access UDIDs. Please update your apps and servers to associate users with the Vendor or Advertising identifiers introduced in iOS 6. You can find more details in the UIDevice Class Reference.
Interestingly, beginning last year, Apple began rejecting apps that access the UDID. Apple hinted that it would begin doing so, but today’s announcement from Apple to developers seems to be the final word on the matter. As pictured above, the iOS Advertising Identifier is a non-personal identifier for iOS devices that developers can access. It does not attach personal information to your device like the UDID system.
Additionally, Apple has announced that, also on May 1, it will no longer accept applications that do not support the iPhone 5′s taller, four-inch display and other iOS device Retina displays.