Hidden in today's release of iOS 5 beta 6 was a key change that blocks developers from accessing UDIDs. This unique device identifier is an important tool to developers and other third-parties for tracking user behavior. However, the move will help alleviate privacy concerns over how developers and ad networks track users without their knowledge or consent.
The UDID works like a unique serial number that identifies a device to a mobile network. Regardless of the user or the app that's currently running on a particular device, the UDID remains unchanged. Developers have used UDIDs to specify certain devices for testing beta apps by registering the UDID with Apple. UDIDs can also be used to record what device is using a particular app and ad networks usually use the UDID to track the use of mobile devices.
With this change, developers and other third-parties will now have to create a unique identifier specific to their apps, which would work much like browser cookies. This could prevent analytics firms from more effectively tracking usage of an app or to cross-reference user data from multiple apps. This will also make it difficult for developers to track if a device has installed or deleted their apps as users could clear any app-specific tracking numbers similar to how browser cookies can be deleted.
[via Apple Insider]