When Apple originally announced phasing out device-specific UDID API, I proposed they instead do a change in what the UDID call returns which would provide privacy for users and tracking for developers: generate the UDID based on the application bundle ID and device UDID, in a manner where if the user deletes and reinstalls an application, the UDID would not change.

However, as the ID would be unique to each application, tracking user behaviour across applications would not be possible unless the user identified himself in a manner that’s shareable, at which point the user should understand cross-application tracking is possible. Also, for certain uses, like banning device IDs of game cheaters, would be possible with this API change.

There’s speculation that Apple will introduce changes to APIs that provide