A “superhuman” AI is just a machine, a very expensive one. It can be turned off and we control the outputs it has. Why would an AI have the ability to launch nuclear weapons unless we gave it a button? A “superhuman” intelligence is without a body, so we control any interfaces it has access to. The Internet could be accessed, but any attempt to “hack” through the Internet is met by routine packet defenses. The AI is still governed by physical laws and would only have so much “free” computation power to do things like script a hack. Perhaps it could do that kind of thing more efficiently.

Maybe in the far, far future when we have androids which can house an AI we will have to worry. But designing a body is one problem. Designing an intelligence is another.