What is a UDID and do I have one?
24th January 2020

UDID stands for unique device identifier. It is a number that is unique to your device like a serial number or IMEI number, but far longer and far harder to guess as it has up to 40 letters and numbers. If you’re an Apple device user, then you will have a UDID number. 

If you own an Apple device, you have a UDID!

UDIDs are commonly used by developers to help them find bugs and crashes by isolating a single device through the use of a UDID. They are also used when you download a free app off of the app store. Ever wondered why when you open an app you see lots of ads tailored to you? How did they get there? How does this app know I was looking at trainers earlier today? They found out through your UDID. 

How do I find my UDID? 

Finding your UDID is pretty simple. All you need to do is plug your device into a computer and copy it out of iTunes. On the panel on the right-hand side, you should see a header named ‘devices’, and your plugged-in device should be displayed there. Click on your iPhone’s info and summary, and click on the ‘serial number’ section. Your UDID should then be revealed as an ‘identifier’. Easy! 

Can a UDID be misused? 

UDIDs have been used for years with no privacy problems. Apps that use your UDID to tailor ads to you can do so because you agreed to it by downloading the app in the first place. There is a strict criteria that apps need to meet before Apple approves them. The issue lies because third parties have access to your UDID, and what they can do with that is potentially quite extensive.

Our devices hold lots of our private information

Your iPhone holds pretty much all the information in your life. Your contracts, your emails, bills, banking info, location, messages and probably at least a few of your secrets! Downloading an app for free means you are selling your UDID, and by default, all of the above. That means advertisers can track your device’s patterns and cater ads to suit your preferences better. This is made so much easier because each UDID is unique. 

The journey is as follows: the developer building an app you are using sells your UDID to advertisers, and they keep your UDID on their servers. When you download another app, the same cycle happens, which means your UDID is more easily traced to reveal your recent activity. And there you have it, those trainers you were looking at on Amazon earlier are displayed right there on the side of your screen. 

Will the UDID privacy model change?

For a long time, we’ve been hearing people saying ‘How does this app know what I’ve been Googling?’. The wider public has clocked onto the fact that their data is being used in some way to influence their internet browsing activity and purchasing decisions. Of course, this ties in with the introduction of GDPR in 2018. We are becoming wiser to where our data is shared. Apple has reacted, and iOS users will be happy to know they are knuckling down on how iOS apps handle users personal information. The decision is that app store developers and advertisers will no longer be able to trace UDIDs. If they do, the app will get removed from the App Store for violating the rules. 

Developers of an app sell your UDID to advertisers

The problem isn’t that we are sharing our data because to download an app we know what we are getting into, it’s that we don’t know how exactly they acquire our information, what they do with when storing it on their servers and how MUCH personal information they can to access from our UDID. This also isn’t the UDIDs fault, as all devices need a way of being identified. It’s more that the UDID is just another way in which iOS has been negligent with their security in the past (more of which you can read about here!).

In the end, advertisers will need to cater ads to specific markets some way or another in future, so will try and find new ways of doing so regardless of the demise of the UDID.