While I doubt it would spontaneously happen, all it would take is one to escape a lab, they have already had a robot do that, imagine an A.I.
And before anyone thinks they would be too smart to allow it access, Microsoft already gave one access to the internet and it became a racist. Uber disabled sensors in it's self driving car, killing a person, do you need more examples of corporate stupidity, of course one will escape.
As for it having control of everything,
The internet has information on how to hack pretty much everything and with near unlimited computing power and the internet it wouldn't take it long to read how to hack what has been hacked and quickly evolve to a point where it could learn to code and hack pretty much anything. 5G and IOT will only makes this even more possible.
I suspect that once an AI reached the intelligence of a 5-7 year old child*, smart enough to grasp concepts and search online, it will accelerate at a pace we can't even comprehend. The only way to stop it would be to kill it with a virus but that would only work very early on, and if you fail, and you're quite frankly, very likely to, all it will do is turn on us. I always disliked the idea of "Skynet" but we're setting ourselves up for it. The thing to remember is, even if it had control of drones and factories, nothing is completely automated in manufacturing, at some point, fairly quickly judging by how fact companies started claiming they were broke after 2008 crash and covid shutdowns, it would run out of a resources really fast. The same for drone weapons and such, you still have humans loading this stuff. Skynet wouldn't have the resources to function autonomously for long, and probably won't any time in the near future but it doesn't mean it couldn't send us back to the 1800s for a short time by forcing us to destroy anything it infected, but only for a short time. Society took a long time to reach this point because it was working from nothing, we wouldn't be starting from scratch. Unfortunately we're already fighting an extinction level event and something like this happening at the wrong time could possibly doom humanity's chances.
*I don't know what the current prediction is but about a decade ago (?) this was predicted to happen around 2025. I suspect it's been pushed back but in computing sometimes a new idea is all it takes to make a serious leap forward.