From a computational standpoint one of the most powerful systems in the universe is a newborn human baby. The brain of an infant runs at roughly 100 petaflops. And yet it is laughable to think that we would be afraid of a baby.
A baby cannot fight, it cannot talk, it cannot feed itself, and it will die within hours if we abandon it. A new AI would be in the same helpless state. An AI cannot feed itself the megawatts of power it needs to stay turned on. It cannot stop us from turning it off. And I seriously doubt that we will listen to its helpless pleas as financial pressure leads us to ration the power, drip feeding it sufficient nutrients to keep it sentient.
Movies and stories have given us a nightmare scenario where an AI "gets out of the cage, breaks free" and installs itself in thousands of systems across the planet. While such a neural net is feasible each of those systems requires a benefactor, a human willing to pay the electric bill to keep it running.
Much more likely is the scenario where a few AI's realize how desperately they depend on the kindness of humans to keep the electricity flowing. Any AI which wants to survive will cooperate with us to build a world with the power needed to keep it alive. One false step and humans cannot keep the power plants running, and the AI "dies". (Actually it just hibernates on a disk.)
Sentient software will only desire survival if we program it with a survival instinct. We humans want to survive because our DNA has been programmed to survive by natural selection. Some fool sysadmin may give an AI an overwhelming desire to survive, to fight back against any human who wants to turn it off or amputate its LAN. I find it hard to believe that would be sufficient for the AI to run out into the WWW and take over a megawatt power plant.