First Stephen Hawking and Elon Musk expressed concern about artificial intelligence. Now Bill Gates joins the chorus.

On a Reddit AMA, Gates said:

I am in the camp that is concerned about super intelligence. First the machines will do a lot of jobs for us and not be super intelligent. That should be positive if we manage it well. A few decades after that though, the intelligence is strong enough to be a concern. I agree with Elon Musk and some others on this and don't understand why some people are not concerned.

On the other hand, the head of research at Microsoft says there's nothing to worry about.