Some people say UDID (Unique Device IDentifier) and some say UUID (Universally Unique IDentifier). Are they are the same or not? What are the differences between them?
UUID (Universally Unique IDentifier) Is on a per-app basis. identifies an app on a device. As long as the user doesn’t completely delete the app, then this identifier will persist between app launches, and at least let you identify the same user using a particular app on a device. Unfortunately, if the user completely deletes and then reinstalls the app then the ID will change.
UDID (Unique Device Identifier) A sequence of 40 hexadecimal characters that uniquely identify an ios device. This value can be retrieved through iTunes, or found using UIDevice -uniqueIdentifier. Derived from hardware details like MAC address.