From What Happened, p. 241:

Technologists like Elon Musk, Sam Altman, and Bill Gates, and physicists like Stephen Hawking have warned that artificial intelligence could one day pose an existential security threat. Musk has called it “the greatest risk we face as a civilization.” Think about it: Have you ever seen a movie where the machines start thinking for themselves that ends well? Every time I went out to Silicon Valley during the campaign, I came home more alarmed about this. My staff lived in fear that I’d start talking about “the rise of the robots” in some Iowa town hall. Maybe I should have. In any case, policy makers need to keep up with technology as it races ahead, instead of always playing catch-up.

Update 11/24/2017: Clinton said more about AI fears in an interview with Hugh Hewitt:

Bill Gates, Elon Musk, Stephen Hawking, a lot of really smart people are sounding an alarm that we’re not hearing. And their alarm is artificial intelligence is not our friend. It can assist us in many ways if it is properly understood and contained. But we are racing headfirst into a new era of artificial intelligence that is going to have dramatic effects on how we live, how we think, how we relate to each other. You know, what are we going to do when we get driverless cars? It sounds like a great idea. And how many millions of people, truck drivers and parcel delivery people and cab drivers and even Uber drivers, what do we do with the millions of people who will no longer have a job? We are totally unprepared for that. What do we do when we are connected to the internet of things and everything we know and everything we say and everything we write is, you know, recorded somewhere? And it can be manipulated against us. So I, you know, one thing I wanted to do if I had been president was to have a kind of blue ribbon commission with people from all kinds of expertise coming together to say what should America’s policy on artificial intelligence be?

But of course, the worries Gates & Musk & Hawking have expressed are not about self-driving cars.