Study: Effectiveness of Apple's App Tracking Transparency
7 min read
fairly easy
Does it stop third-party tracking? Or is it just an illusion of privacy?
This study, conducted by Lockdown Privacy, was featured and summarized by The Washington Post in September 2021.


In April 2021, Apple released the App Tracking Transparency ("ATT") feature with iOS 14.5. ATT claims to give users choice and transparency for third-party tracking in their apps, and it was lauded by many as a step forward in protecting user privacy. Does it really work? Five months after its release, we tested ten of the top apps in the App Store to see if ATT succeeds in stopping tracking.

Using the open source Lockdown Privacy app and manual testing, we found that App Tracking Transparency made no difference in the total number of active third-party trackers, and had a minimal impact on the total number of third-party tracking connection attempts. We further confirmed that detailed personal or device data was being sent to trackers in almost all cases. ATT was functionally useless in stopping third-party tracking, even when users explicitly choose "Ask App Not To Track".

Who We Are

We're ex-Apple engineers whose mission is to increase transparency in technology. We've spent the last four years creating open source privacy software (Lockdown Privacy), writing informative content (Transparency Matters, Privacy Review, Openly Operated), and building free tools to help developers become more transparent (OpenAudit).

Unlike most privacy companies that ask users to trust their unproven Privacy Policies, everything we build is open source, so all the results and data in this report can be replicated and verified by anyone with an iOS device. And because we're also Openly Operated, all our claims are fully backed up by source code, infrastructure, and audit trails — verifiable by anyone with an internet connection.

Background + Objective

It's no secret that Apple tries to brand itself as a privacy-conscious counterpart to its rivals Google and Facebook, whose ad-based businesses are inherently at odds with privacy. This privacy-as-marketing…
Johnny Lin and Sean Halloran
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