iOS 6 Introduces the IDFA

What Changed

In the early years of smartphone apps, advertisers and analytics companies tracked people with permanent device identifiers, as the EFF's history of the ad ID explains.¹ On iPhone that was the Unique Device Identifier, or UDID: a fixed code tied to the hardware that a user could never change or remove. Apple had already marked it as deprecated for developers in iOS 5 in 2011, without saying what would replace it.²

With iOS 6 in September 2012, Apple replaced it for advertising with the Identifier for Advertisers (IDFA). The IDFA was a separate ID made for ads, and users could reset it at any time, which broke the link between their old activity and new activity. Apple's developer documentation still describes the IDFA this way.³ After a year of warnings, Apple stopped accepting new apps and updates that read the UDID from May 1, 2013.⁴

iOS 6 also added a Limit Ad Tracking setting. It didn't stop apps from reading the IDFA. Instead, apps received a flag telling them the user had opted out, and Apple's rules said they should then use the ID only for limited purposes such as frequency capping and attribution.

Why It Mattered

The IDFA set the pattern for mobile advertising for the next decade. It gave the industry a sanctioned, shared identifier that worked across every app on a device, so ad networks could connect an ad seen in one app to an install or purchase in another. Attribution vendors, retargeting and app-install advertising were all built on it.

It also introduced the idea that the user, not the device, should control the identifier. That control started out weak: resetting was buried in settings, and opting out was a request rather than a block. Each later step in this timeline turned that preference into something firmer, from zeroing the ID in iOS 10 to requiring permission in iOS 14.5.

Google followed with a resettable Advertising ID on Android the next year, so both mobile platforms ended up with the same model.