In this case it's not like the devices were turned off, they were put on "defrost" which means heating up to 50°C (122°F). Why would you need the ability to remotely set all your fridges to defrost??
replyOne possibility is that it’s maybe useful for the fleet operator to be able to remotely update firmware and the attacker used that.
replyThe other, more likely, answer is that there’s a diagnostic mode that allows raw control of the system and no one bothered to require physical presence to enable service mode.
With remote firmware update capability, at attacker could easily brick the entire fleet. With just service access it could be possible but would be more complex.
I remember having to do this every few hours 25 years ago when working at a store part-time as a student.
replyHaving networked telemetry seems like a good idea, just not sure why they would need remote control too - that seems far more dangerous than necessary.