why would it need to reproduce? An AI could conceivably control most of the devices on the entire planet, set up subroutines, trigger cascade effects..why would it remain where anyone could physically harm it? An intelligent AI could easily trick people into building it it's own hardened "fortress"...It could transfer funds, "hire" people to do things for it, who would never know what they were actually doing, or even that they were working for it...and then delete all records of it...
I'm not looking for skynet, i'm not suggesting that any of this is imminent, but don't even try to tell me that it isn't a possibility.
Human beings have so much arrogance, and so little sense, I am amazed that we haven't immolated the entire planet hundreds of times over with no help at all.