The intentions of app developers are difficult to gauge sometimes. They can invent wonderful software that makes you wonder how you ever lived without it, or they can create privacy nightmares at the same time. Adjust, AppsFlyer, MoEngage, Localytics, and CleverTap are app developers that offer uninstall trackers that remind you of long uninstalled apps. They will remind you of a new updates to T-Mobile, Spotify, Yelp and more as they pester you with notifications as to why you should reinstall those apps ASAP! They can remind you over and over again as you visit websites because they exploit the push notification services built into iOS and Android. The push notifications were meant to let you know that you have a new email or update without bothering you. The creators of the uninstall tracker apps say that they are meant to gauge user reaction to app updates and changes. They can do this because users gave their permission to freely use their data long ago. Apple and Google had no comment when asked if this was the intended usage of push notifications. Developers have always been able to use so-called silent push notifications to ping installed apps at regular intervals without alerting the user--to refresh an inbox or social media feed while the app is running in the background, for example. But if the app doesn't ping the developer back, the app is logged as uninstalled, and the uninstall tracking tools add those changes to the file associated with the given mobile device's unique advertising ID, details that make it easy to identify just who's holding the phone and advertise the app to them wherever they go.