Simon Willison’s Weblog

Is there a way to uniquely identify the device of the user that are connecting to a web app or a website?

6th November 2012

My answer to Is there a way to uniquely identify the device of the user that are connecting to a web app or a website? on Quora

If the device is a mobile phone running an app it’s very easy to create a permanent identifier for the application/device—it can be generated once the first time the user runs the app, stored locally and then passed to Facebook with every future request. Think of it like a browser cookie, but unlike browsers the app developer can ensure the cookie is never deleted once it has been created.