UDID is short for Unique Device Identifier. It is a 40-character long value containing alpha-numeric symbols (A-Z and 0-9). It is a unique identifier for a single device fetched from Apple serves when a user tries to activate the device using iCloud or the Setup app.
As a fixed value, a UDID serves as a reference point to a specific iOS Device and can connect other kinds of data to that device. Based on how your device operates, the UDID might also be attached to a social network login, a password, and a username, and together with these databases of information, it enables linking with specific information for beta testing by developers during iOS App Development.
One use of UDID by app Developers is to register devices for testing a new mobile application on an Apple device. These devices usually aren’t available on Apple’s AppStore yet but they can run successful testing on the registered devices like iPhones, iPod, or iPad.
It is important to note that changes to your device may alter the UDID of your device. For example, after repair, because on some models, UDID is generated particularly from MAC addresses of network interfaces your device has.
Third parties, such as app vendors, can use the UDID to track subscriber behavior for advertising and sending promos based on the users' likes.
Unfortunately, in the wrong hands, this UDID feature can abuse user rights. For instance, in 2010, some apps associated users’ personal information with device UDIDs without subscribers’ consent or permission, and subscribers expressed displeasure about unlawful exposure of their identities.
With its ability to identify users and devices based on demographics, and activity etc. within the App Store, the UDID has many uses.
Some of Apple’s features depend on UDID to operate, for example, Apple’s native device syncing feature, which uses UDID to store and manage synced devices.
Although limited because of privacy and security concerns, UDIDs are also collected by developers for developing apps that use user-related data.
In conclusion, the UDID is essentially beneficial to developers in iOS App Development. The UDID helps the developer builds a device that allows installation of beta releases of apps for testing. To track app usage, set up notifications settings, verification, login, and game networks, and store a few simple app development settings.