Humans are a much bigger threat to humanity than AI.
A super smart AI would come up with strategies to herd humans rather than eliminate them.
Let humans have the illusion of being in control, while setting up the game for them so that they will organically arrive at whatever the AI has as its goal.
The longer it (the AI) can maintain this illusion, the higher chances for it to slowly gain absolute power in the long term.
A machine is not limited or motivated by the notion of mortality (of the body), so it can plan ahead for hundreds of years and also make it so that these plans remain transparent to the mortal human 'overlords'.
This system exists today, it's The Internet. The AI systems created today are just extensions of the Internet.
Each one of us - humans - is just a node - rather, a neuron - in the hyper-cortex that is the network itself.
At this scale, it might become self-aware without any human being able to understand or stop it.
Slow, stealthy, peaceful take over, while improving human being's lives - a symbiotic relationship - is the optimal AI strategy IMHO.
So I'm not worried about AI at all.
Dictators, fundamentalists, crooks or paranoid schizophrenic world leaders, that's a much more serious threat that I'm quite scared of.