The UDID is a feature of Apple mobile devices and stands for Unique Device ID that is made up of a sequence of 24 to 40 characters.
Why Do You Need a UDID?
We get your unique device UDID to enable app installation process and to connect your Subscription with the device. We also need to recognize your device to make initial arrangements on our site to set your account up and running.
Device UDID is also required for any support operation and we may ask you to provide it.
Note: providing device UDID doesn’t endanger your security.
Profile installation makes no changes in your initial system, and it doesn't get access to your private info stored on the device.
How To Find Your UDID?
We recommend you to use this web-based tool: http://get.udid.io/