The UDID (Unique Device Identifier) is used by many applications to establish a unique ID for your mobile user on iOS. Some apps, like Ad Networks, will persist the UDID to track app usage across all the apps on your phone. Given recent Federal attention regarding privacy concerns, Apple is accelerating their plans to kill off the use of UDID in apps. While Xtify never used the UDID in this fashion, we are complying with this mandate and will issue a patch this week that replaces our non-essential use of UDID. We will post again when it is available and send out a newsletter to our opt-in subscribers.
For more information, TechCrunch posted a great article that discusses UDID.