A unique device identifier (UDID) is a 40-character string assigned to certain Apple devices including the iPhone, iPad, and iPod Touch. You can find it from iTunes. Your iPhone can only install programs that are approved by Apple. The UDID is being used by developers to register devices for testing their Apps. Only on registered devices developers can run Apps that are not in Apple's AppStore yet.
Remind that there is only one UDID number through your iPhone or iPad lifetime unless you changed any parts (motherboard) of it.
You can also get your UDID from iTunes when you connect your iPhone or iPad to Mac desktop. But here is the very easy way to get UDID in just one click from your iDevice safari browser and install (temporary) the profile to show up your IMEI and UDID numbers.
We are using Apple Mobile Device Management concepts to provide you information about your device. Always remember that profile you install tells your iPhone, iPad or iPod to send encrypted data (UDID, IMEI, and Serial No.) to your browser.
This profile is temporary in nature and exists on your device only do few moments work to send encrypted data. And it shall be automatically removed from your iOS device after encryption happened. We do not store or reuse any of your device information.
To check any profile installed on your device just go to Settings>General>Profiles. If you didn’t find any such profiles, there is nothing installed on your device.
Apple permits us to get UDID, IMEI, Product Name and iOS Version, but just as a matter of ethics getudid.io doesn’t access it. So stay safe when you are trying apple UDID registration. We are believers of ethics.