Apple has now explained its recent privacy updates that prompted widespread questions from the digital advertising sector. The firm released details in a blog post outlining new limits on tools that identify and follow users across sites. These updates apply via WebKit, the engine behind Safari on iPhones and iPads.

The changes focus on identity resolution techniques. Adtech firms use these to link details like email addresses, phone numbers, IP addresses, browsing patterns, and device data for tracking users across devices. Such methods gained traction as browsers phased out third-party cookies traditionally used for targeting and measurement.

Apple noted that people often share an email to access a site or newsletter but do not anticipate it being passed to other firms for hidden tracking. The post stated that blocking cross-site cookies alone is insufficient because trackers have shifted to post-cookie methods, prompting stronger safeguards in recent releases.

The update introduces domain-level blocking to stop identity providers from bypassing rules by altering data transmission. Earlier this month, Apple quietly blocked domains from firms including The Trade Desk, LiveRamp, ID5, Permutive, and Audigent. This initially halted The Trade Desk ad serving on Apple browsers, though a fix later restored ad delivery while keeping the identifier restricted.

The advertising sector prepares for wider effects

The industry now anticipates effects as more users adopt iOS 27. Experts expect reduced reach for advertisers on the open web, along with higher costs for remaining audiences and greater challenges in frequency control and campaign measurement.

Identity resolution appears on most open-web sites. Research analyzing hundreds of thousands of domains showed over 83 percent using alternative identifiers by mid-2025. Reduced effectiveness could shift budgets toward walled gardens such as Meta and Google, which rely less on these tools due to their own user data. Apple itself operates growing ad businesses in its App Store and apps like News and Maps.

Apple signals continued enforcement

Questions remain about Apple's precise criteria for identity resolution providers, and the firm has shown it can expand blocks without advance notice. Reports indicate a broader dynamic list that could affect hundreds of adtech, martech, and data firms, with impacts appearing only after disruptions begin.

Apple linked to its tracking prevention policy, which notes possible side effects on site funding, ad measurement, and fraud detection. The policy emphasizes that user benefits take priority when tradeoffs arise. Since introducing Intelligent Tracking Prevention in 2017, Apple has faced ongoing workarounds from adtech firms seeking to balance monetization and privacy. The company treats attempts to evade its measures as seriously as security exploits and may impose further limits without warning.