It's by Nick Bostrom[0].

He's the same guy that wrote 'Superintelligence: Paths, Dangers, Strategies'[1]; which is reportedly the book which 'alerted' Elon Musk to the dangers of AI.

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[0] http://en.wikipedia.org/wiki/Nick_Bostrom

[1] http://en.wikipedia.org/wiki/Superintelligence:_Paths,_Dange...