Apple has been using this IDFA (Identifier for Advertisers) for ‘ever’. As an app developer we see this each time we publish an app. If you want to integrate ads this is the ID that allows 3rd parties to track your usage. It goes without saying that Apple keeps a close eye on it as well. Now Europe is saying Apple is in clear violation of GDPR regulations. The real problem for apple isn’t allowing users to opt-in or not. They can do that easily. The problem is if a user opts-out, they opt-out of tracking for all of the app installations which use this identifier for their ads. And why give away a free app, if you can’t push ads… This Reuters article is decent.