From Apple If you go to Privacy Settings / Permissions and turn off Apple, this should be blocked. Why do you have these options, too?
So does Apple. In iOS, you can request an ID that you can use to track a user for advertising purposes. If you indicate that you do not want to be tracked, this ID cannot be read.
What these companies do is combine a lot of other information about your device that is not intended to track users, and cannot be used for that purpose on their own, until they have enough data to identify the user anyway.
There are about 1 billion iPhones in active use, imagine an app checking how much storage space you have and notice that you have a 128GB iPhone. How many people own a 128 GB iPhone? That’s a lot less than 1 billion, so let’s say 100 million for the sake of simplicity. They can see that your iPhone is connected to the KPN network in the Netherlands. iPhone 128 GB on KPN in Netherlands. Maybe that’s 500 thousand. They also see that you have an iPhone Xs Max. iPhone XS Max 128GB on KPN Netherlands. How much would that be? 50000? Suppose you can no longer see very well and move the text two steps larger. iPhone XS Max 128GB on KPN Netherlands with Two-Step Text larger than usual. How much is left?
Each piece of information, in itself harmless, makes the group smaller. If you have enough of this kind of information together, you can eventually associate it with a single user.
Apple can’t block this, as this is about information that apps need to function, and that in and of itself isn’t privacy sensitive. If the app can no longer read if you want the text larger than the standard, the app will not take that into account.
So it is not technically possible to prevent fingerprints. You have to address this by tracking this and getting those apps out of the App Store.
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