Apple in a recent update to the documentation for iOS 5, which is only available to registered Apple developers, Apple alerted developers that the company is in the process of deprecating access to the uniqueidentifier alphanumeric string that is unique to each iOS devices such as iPhones and iPads.
Many apps and mobile ad networks, for instance, uses the UDID or a hashed version to keep track of who their users are and what actions they have taken. App publishers are now supposed to create their own unique identifiers to keep track of users going forward, which means they may have to throw all of their historical user data out the window and start from scratch -- as the company "recommends developers create a UDID specific to apps."
Obviously, UDIDs were a security threat as marketers and advertisers (and worse) could follow your usage patterns and gather data through different apps.
Quote from Apple's Developer documentation:
Deprecated in iOS 5.0
An alphanumeric string unique to each device based on various hardware details. (read-only) (Deprecated in iOS 5.0. Instead, create a unique identifier specific to your app.)
"The change may be in response to privacy concerns or as a way to pre-empt them. Mobile ad networks, for instance, use the UDID to target ads. It is not clear whether Apple itself will stop relying on the UDID as a unique identifier for iAds, Game Center or other services," noted TechCrunch.
However, it seems Apple likely will continue to use the UDID for its iAds, GameCenter, subscriptions and other services it offers across iOS devices, or so one industry CEO thinks:
"I guarantee Apple will not stop using UDID," predicts one mobile industry CEO. If Apple does continue to use UDID for itself but denies it to developers that would be an "extremely lopsided change." It would give Game Center and iAds yet one more advantage over competing third-party services."