https://techcrunch.com/2018/06/05/apple-got-even-tougher-on-ad-trackers-at-wwdc/

Apple unveiled a handful of pro-privacy enhancements for its Safari web browser at its annual developer event yesterday, building on an ad tracker blocker it announced at WWDC a year ago.

The feature — which Apple dubbed ‘Intelligent Tracking Prevention’ (IPT) — places restrictions on cookies based on how frequently a user interacts with the website that dropped them. After 30 days of a site not being visited Safari purges the cookies entirely.