Open Graph is a language for structuring content and sharing that goes on in other apps, and we're continuing to build it out longer term. But we found we need to build more specific experiences around categories like music or movies. Where we've taken the time to build those specific experiences, stuff has gone quite well.

Now the playbook is we build AI tools to go find these fake accounts, find coordinated networks of inauthentic activity, and take them down; we make it much harder for anyone to advertise in ways that they shouldn't be.

When I'm introspective about the last few years I think the biggest mistake that we made, as a company, is betting too much on HTML5 as opposed to native... because it just wasn't there. And it's not that HTML5 is bad. I'm actually, on long-term, really excited about it. One of the things that's interesting is we actually have more people on a daily basis using mobile Web Facebook than we have using our iOS or Android apps combined. So mobile Web is a big thing for us.

We're a community of a billion-plus people, and the best-selling phones - apart from the iPhone - can sell 10, 20 million. If we did build a phone, we'd only reach 1 or 2 percent of our users. That doesn't do anything awesome for us. We wanted to turn as many phones as possible into 'Facebook phones.' That's what Facebook Home is.

Facebook originally got started around the same time as a bunch of the early smartphones and those platforms got started. So we didn't really get to play any role in developing that platform.

So I think that the scale of the systems has created this responsibility for us, where we have to be more proactive about finding and addressing issues [harmful content]. And we can do that both by building technology that is possible now, but wasn't even possible five or ten years ago, and by hiring people at a scale that would not have been possible for us before.