Apple’s latest privacy crackdown has the online advertising industry scrambling for answers. Now, the tech giant is finally offering some.
Late Monday, Apple published a blog post laying out the rationale for the new restrictions, which are designed to block technology used to identify and track consumers across websites. These changes are implemented through WebKit, the browser engine that powers Safari and other browsers on iPhone and iPad.
Apple said the change is intended to target “identity resolution,” a method used by ad tech companies to connect individual data points about users, such as email addresses, phone numbers, IP addresses, browsing history or information about the device they are using, to identify and track them across devices.
The approach is growing in popularity as many web browsers, including Apple Inc.’s Safari, begin phasing out third-party tracking cookies, which are small files placed on a user’s device and traditionally used for web tracking. The advertising industry deploys tracking to pinpoint specific audiences and measure whether their campaigns are effective.
Apple said in its blog post that while users might easily provide their email address to log into a website or sign up for a newsletter, most people wouldn’t expect it to be shared with other companies for invisible tracking purposes.
“Today, simply blocking cross-site cookies to prevent cross-site tracking is not enough, because the tracking industry has not stopped trying to track users across the web,” Apple said. “They have entered the so-called post-cookie era, and in our latest version, we have put in place strong protections.”
The blog post explains that Apple is implementing “domain-level” blocking, a broad intervention designed to ensure identity providers cannot circumvent restrictions by changing the way they send data.
Earlier this month, Apple startled the ad tech industry when, without warning, it began blocking domain names run by several companies that provide alternative identifiers. Blocked domains include those operated by The Trade Desk, LiveRamp, ID5, Permutive and Audigent.
The initial rollout also blocked The Trade Desk’s ability to serve ads on browsers run by Apple. A few days later, Apple rolled out a fix that restored The Trade Desk’s ad serving domain and its advertising identifier, Unified ID 2.0, from being blocked.
The advertising industry is bracing for the fallout
As more and more users start updating their devices to iOS 27, the advertising industry is now bracing for the impact. Advertising professionals previously told CMO Insider that the change would make it more difficult for advertisers to identify and reach users over the open web.
By effectively narrowing the pool of users they can target, advertisers can expect to have less reach and higher prices to reach an audience they can still identify, and it will be harder to control how often people see ads and measure whether their campaigns are effective, industry insiders say.
Identity resolution has become widespread in the open web. An academic paper published in September analyzed 600,000 websites over 41 months and found that 83.76% of them were using alternative identifiers by May 2025.
If advertising becomes less effective on the open web, marketers can put more budget into so-called “walled garden” platforms like Meta and Google, which don’t rely heavily on alternative identifiers because they have large amounts of their own logged-in user data. Apple’s advertising business is also growing in its App Store and in its apps, including News and Maps.
Apple isn’t backing down
There are still open questions about Apple’s exact definition of an identity resolution provider, and the company has proven that it can add domains to its blocked list without warning.
There are also signs that Apple is just getting started. AdExchanger first reported that Apple has also created a broader block list that dynamically blocks potentially hundreds of ad tech, marketing tech and data companies. Affected companies may not realize they have been added to the list until they start experiencing disruption.
In a blog post on Monday, Apple mentioned its long-standing anti-tracking policy, which acknowledges that its blocking rules can have unintended effects. These include disrupting funding for sites that use targeted or personalized advertising, ad measurement and fraud prevention.
The policy states that while Apple will try to limit unintended impacts, “when faced with trade-offs, we generally prioritize user interests over preserving current site practices.”
Ever since Apple launched its Smart Tracking Prevention feature in 2017, the tech giant has been locked in a cat-and-mouse game with the ad tech industry, which has been developing workarounds for its privacy updates. Ad tech companies believe these technologies are necessary to help publishers effectively monetize ads on their sites while still maintaining user privacy.
Apple has long believed that “privacy is a fundamental human right” and has made clear in its policies that it will not allow workarounds within its purview.
“We take circumvention of shipping anti-tracking measures as seriously as exploitation of security vulnerabilities,” Apple’s policy states. “If a party attempts to circumvent our tracking prevention methods, we may add additional restrictions without notice.”