Apple to begin rejecting apps that access UDIDs
Apple has informed developers that it will begin officially rejecting newly submitted and updated applications that access the iOS device UDID. Apple says that this new policy will begin on May 1st. With iOS 6, Apple began offering developers a new Advertising Identifier system that replicates the use of UDIDs for developers. Apple recommends that developers move over to this new system.
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.