Preview at WWDC likely in June, followed by September launch.
Apple Begins Rejecting Apps for Using the Unique Device Identifier (UDID)
As the name suggests, the UDID is a unique identifier for every iOS device. It's tied specifically to the hardware and can't be changed by the user. Apple had previously warned developers with the introduction of iOS 5 that the use of the UDID was deprecated and would be phased out. The sudden rejections, however, have caught some developers off guard:
“Everyone’s scrambling to get something into place,” said Victor Rubba, chief executive of Fluik, a Canadian developer that makes games like Office Jerk and Plumber Crack. “We’re trying to be proactive and we’ve already moved to an alternative scheme.” Rubba said he isn’t sending any updates until he sees how the situation shakes out in the next few days.The reason for the phasing out of UDIDs from developer use is due to increased pressure on Apple due to the privacy implications. Apple and several App developers have been sued over the use of the UDID to track users across different apps. While the UDID doesn't specifically identify a user, the sharing of UDIDs across ad networks and apps can help piece together a valuable picture of activity and interests of the user of a specific device. Apple seems to be requiring apps to generate their own unique identifiers for each installation to avoid this ability to share such information across apps.