According to AdExchanger, T-Mobile has started selling its customers’ app usage data to third-party advertisers.

The action is carried out via a program called App Insights, which allows third-party advertisers to purchase the usage data of T-Mobile customers and use it for advertising purposes.

The App Insights program allows advertisers to target T-Mobile customers based on the apps they have installed on their phones and the usage patterns of those apps. The websites users visit and the WiFi networks they connect to are also important indicators for advertisers.

The program is aimed at Android users with iOS users excluded from the program. This is partly because Apple has an App Tracking Transparency (ATT) framework that makes it difficult to track users.

The program is not mandatory because users can unsubscribe. Users can download the “Magenta Marketing Platform Choices” app to see which companies have access to their data and opt out. You can also download App Choices, another app that allows users to opt-out of data-sharing programs.

However, despite calls to prevent technology companies from illegally using user data without their permission, some technology companies openly share this data with advertisers.