With its most recent Safari browser release for iOS and MacOS, Apple has introduced “Intelligent Tracking Prevention”, in a move that significantly reduces the value of ad impression opportunities in Safari mobile/desktop browser and in-app webview environments.

The announcement was made last week at the company’s annual conference for software developers, and one advertising agency executive has claimed it puts Facebook and Google in a ‘precarious place’. This is because it would block the firms’ ability to follow users across the web as well as attribute how many individual users were clicking on links or what kinds of people were looking at ads.

As IAB Tech Lab explained: “Safari will now block sending cookies to third parties determined to be ‘trackers’.

“This will be highly disruptive to buyers, sellers, and technology platforms, given the role third-party cookies play in audience addressability, segmentation (and thus targeting and personalisation), and measurement. It will also negatively impact consumers, as ads will be less relevant and publishers may struggle to provide content and services.”

Miratrix Founder Nicholas Duddy argued that the development shouldn’t come as any great surprise, and suggested benchmarking traffic.

“I guess the only thing I can say on it is that it was likely to come – Apple are by far the strictest when it comes to gathering data. It will make fingerprinting harder but not impossible.

“In this case I’d benchmark traffic before and after adoption and use the difference between them to forecast more realistic more accurate figures.”

The changes will have the most dramatic effect on mobile usage and tracking. Safari is the second most popular web browser with about a quarter of internet users using the browser on mobile and desktop in the US alone.

It is also of course the default web browser on the iPhone, with Apple selling a massive 52 million of them in the quarter ended 31 March.