For years, Facebook's sneakiest data-collector has been the "Like" button. Any site that wants Facebook traffic needs one, which means they're just about everywhere. And in order to work right, the button needs to log you in — which is to say, it needs to know who you are. How else would Facebook know who liked the post? Even if you don't click, Facebook registers that you loaded the button, which means they get a map of every Like-enabled site you've been to, just the kind of data that advertisers will pay to target against.

Today at WWDC, Apple took a direct shot at that system and Facebook itself. Onstage, Apple's VP of software Craig Federighi described Safari's new anti-tracking features in unusually confrontational terms.

"We've all seen these like buttons and share buttons," Federighi told the crowd. "Well it turns out, these can be used to track you, whether you click on them or not. So this year, we're shutting that down."