I think most people naturally enough assume that any AI capable of destroying humanity would evolve within the Defense community, but why would this be so? Everything is connected. All AI is almost inherently AI on the internet, and anything on the internet can be hacked, and hacked quickly by a sufficiently developed intelligence.
Watch Eagle Eye to get some sense of what is almost certainly possible.
A Facebook AI could destroy the world. A UPS AI could destroy the world. It could start anywhere. This is very dangerous technology. Are we not fat and lazy and underworked enough already?