Addendum: It is explained (from the developers point of view) in the WWDC 2012 session "Privacy Support in iOS and OS X". https://developer.apple.com/videos/w

Addendum: It is explained (from the developers point of view) in the WWDC 2012 session "Privacy Support in iOS and OS X". https://developer.apple.com/videos/wwdc/2012/?id=710 https://developer.apple.com/videos/wwdc/2012/?id=710 The old UDID is splitted into three new API: 1. Application ID, which scope is the app and lifetime is till uninstallation of this app. 2. Vendor ID: scope is developer and lifetime is till uninstallation of all developer's apps. 3. Advertising ID (identifierForAdvertising or IFA): scope is the device and a new ID is created by "Erase all contents/settings" and it is not restored across devices (practically lifetime is lifetime of the device). This means when you start to use a new iPad it will have its own Advertising ID and not use that of your old iPhone, because the ID is not tied to your Apple ID account, but tied to a device. It is noteworthy that after Apple banned the usage of the UDID some developers and ad networks started bypassing Apples privacy rules and made their own open source ID replacement: https://github.com/ylechelle/OpenUDID/blob/master/README.md https://github.com/ylechelle/OpenUDID/blob/master/README.md But I don't know if this will be permitted in the future or you have to use Apples provided ID system (I would assume the latter).