Apple’s iOS device UDIDs are commonly used for advertising and application user tracking in iOS. Earlier this year, Apple announced that iOS 6 will no longer support UDIDs. Instead, UDIDs will apparently be replaced, for advertisers at least, with a new feature called the Advertising Identifier. This identifier, unlike the UDID, does not tie personal device information to the ID. It is also non-permanent. Apple explains in the iOS 6 settings:
Along with this new identifier, Apple allows users to limit ad tracking in iOS 6. Apple says that some advertising systems used by App Store applications may still track information until they are updated to support the new ID system.
