When iOS 14.5 is released, is use of ATTrackingManager required only on iOS 14.5+? — What is the Identifier for Advertisers (IDFA)? The Identifier for Advertisers (IDFA) is a random device identifier assigned by Apple to a user’s device. Advertisers use this to track data so they can deliver customised advertising. The IDFA is used for tracking and identifying a user (without revealing personal information).