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The Identifier For Advertisers (or IDFA) is a UUID string that lets advertisers match the user with their behavior. Each iOS device owner can decide whether they want to be tracked by advertising companies. This allows those companies to supply that user with content that is tailored towards them. Developers who use the IDFA have to make changes in their applications in order to be compatible for iOS14. They will now be required to show a dialog to the user, asking them if they want the application to track them or not.