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Facebook is warning developers that privacy changes in an upcoming iOS update will severely curtail its ability to track users' activity across the entire Internet and app ecosystem and prevent the social media platform from serving targeted ads to users inside other, non-Facebook apps on iPhones.

The next version of Apple's mobile operating system, iOS 14, is expected to hit an iPhone near you this fall. Along with its many new consumer-facing features , iOS 14 requires app developers to notify users if their app collects a unique device code, known as an IDFA (ID for Advertisers).

The IDFA is a randomly-generated code that Apple assigns to a device. (Google assigns similar numbers to Android devices.) Apps can then use those codes to tie together user activity. For example, Facebook, a local shopping app, and a local weather app might all access that identifier. Facebook and other advertising businesses can then use that cross-app use data to place targeted ads for advertisers on other apps, which is what Facebook does with its Audience Network program.