How iOS apps keep track of me across reinstallations?

I installed app MyApp on iOS 15, I uninstalled it and then reinstalled it, the app still recognized my phone. How did it do that?

• iCloud backup is not enabled for this app.
• App data was lost after reinstallation, but it did recognize my phone.
• I did not allow apps to 'Ask to Track'.
• The app limits what you can do with the same phone probably to prevent abuse.

Was the app fingerprinting my phone, or did it have access to some device specific identifers?

Solution 1:

I would say none of the above.

Usually the situation you describe is due to the app saving information into the Keychain on the phone. When you uninstall the app, the Keychain data is not deleted. Therefore when the app is reinstalled, it can load in the data stored earlier.

I assume the app in question really isn't called "MyApp", so that makes it hard to say whether this is actually the case for you. There are other ways something similar can happen, but the above way is by far the most common. If your situation is actually so that you have taken advantage of a "once-only free trial" and want to get another "free trial" by covering your tracks, it can also be because of fuse bits stored at Apple.