https://www.cnbc.com/2018/06/04/apple-limits-safari-tracking-gives-more-control-over-personal-data.html

Apple is introducing more controls to allow Safari to control who gets their personal information online, including limiting data tracking across websites.

The move helps Apple respond to increasing user concerns about privacy online, but could make it harder for websites and advertisers to target ads efficiently. This will have the most dramatic effect on mobile usage and tracking. Safari is the second most popular web browser with about a quarter of U.S. internet users using the browser on mobile and desktop according to the federal government's Digital Analytics Program. It is also the default web browser on Apple's massively popular iPhone. The company sold 52 million iPhones in the quarter ended March 31.