Following increased pressure from US Congress, Apple has begun rejecting new apps and patches that utilise a device's UDID code in order to uniquely identify a user's mobile phone or tablet. Whilst Apple had mentioned around six months earlier in its documentation that the feature would be depreciated, typically a process taking around one year, the sudden rejection of apps utilising this approach for identification has startled developers and ad service providers alike.
Pressure to avoid use of UDIDs came amidst privacy concerns. UDID codes are unique to each and every mobile device; it is not possible to simply change UDID codes by formatting and because it's generally used as a unique key in databases, the UDID often remains in most systems even if other specific pieces of information about a user are removed, making it difficult to shake for those who perhaps wish to be forgotten.
The primary issue for developers now, is that until ad, gaming network, analytic and test service providers update their systems, it's not possible to include any of these elements into an app, preventing the submission of many new 'free' apps and slowing the development process for others. Developers with apps already out on the App Store are withholding updates to avoid their creations being taken down for non-compliance.
Currently, asking users for permission to use their UDID appears to be receiving approval, however this hampers user experience and will no doubt turn away some punters. The issue is that UDID provides a reliable manner with which to identify a user online between applications without requiring some form of registration and login, it's also highly useful in games deploying simple scoreboards or anti-cheat systems.
Many firms are looking to other unique identifiers such as the MAC address of the WiFi module, however new approaches remain unstandardised and share a unique piece of information just like the UDID, simply staving off the issue. Really, what Apple needs to have done prior to blocking its developers, is to update devices, allowing for users to generate a random UDID code and associate it with an iTunes account, enabling reliable tracking whilst offering a user the ability to abandon their UDID if they so wished.