Oh, you've tasked AI with managing banking? K. All bank funds are suddenly corrupted.
Oh, you've tasked AI with managing lights at traffic intersections? K, they're all green now.
Oh, you've tasked AI with filtering 911 calls to dispachers? K, all real emergencies are on hold until disconnected
Whatever a virus is able to do, AI can, theoretically, perform aswell. Ransomware, keylogging, social engineering (I'd argue this one is most likely - just look at people trusting whatever AI spits out with absolute confidence).
When you mentioned nuclear power plants, Stuxnet comes to mind for me.
I don't even think it would have to go that far. Just corrupt my laptop and the 20 or so guys like me across the industrial world. Put a logic bomb to go off in say 10 years. All those plants getting updated and maintained. 10 years from now every PLC fires itself. I could write the code in under an hour to make a PLC physically destroy itself on a certain date.
Social media corruption, blackmail and extortion, attacks on financial exchanges, compromising control systems for infrastructure, altering police records, messing with your taxes, changing prescriptions, changing you to legally dead, draining your bank account.
Given full control over computers some being could easily dump child porn on your personal devices and get a SWAT team to come out. That is just you, I am sure you have family and friends. So yeah you will do what that being says which includes giving it more power
So things that can already happen.
It's also a huge leap to say that anyone will give ai full control over all computers. That's like saying nuclear power is going to kill us all because we're all going to have Davy Crockett tactical nukes. Like I guess that's possible but it's so extremely unlikely that I don't get the hysteria. I think it's articles trying to scare people to get clicks and views.
Listen up, soldier: this is your President. Here are all of the authorization codes, so you know this is real. Launch all of our WMDs at this list of targets that will simultaneously do maximum damage to the targets while still giving them the ability to counterstrike, thus maximizing the overall body count.