I didn't expect to spend so much time today thinking about fridges. I have so many questions. If it's all so connected and monitored and notifies of issues, couldn't it notify anyone that the settings are weird, like continuous 50 degree Celsius defrosting? How much access did the hackers have, apart from temperature controls? Could nobody intervene quickly before the damage was done? Was there a way to "unplug" the fridges or they would just keep frying, so they had to get people across all the stores doing manual resets?

It can do all that IF YOU THINK OF IT and then write the program to do it. If you think of it - which is unlikely because it never happened before (or perhaps it did before but electronics are reliable and so you think it won't ever again).

These are commercial units. There is no plug. There is a circuit breaker in the back room, but general rules is only an electrician is allowed to touch them: if they are off there is always a good reason (until now) and so random staffers touching the panel to turn a breaker on is likely to kill somebody.

Look for "Danfoss AK-SM 720 user manual" and scroll through the pdf.

You'll find that these are quite complex control systems and their data may not be integrated into an operational or security control centre. So if they are not configured for, or resourced (in terms of operators), to handle anomalies, how do they notice and respond?

Without knowing anything about the attack it may be that the controllers were not connected directly to the public Internet, but an on-site VPN that became compromised some other way. Or with a compromised laptop of a technician that connected.

So while you are thinking about fridges today, think about how you would secure and operate control systems across tens of thousands of stores. Would that be easier without Internet connectivity? How do you get qualified and experienced technicians into each (air gapped) store? Another complexity is that many of these systems are part of facilities management systems (HVAC, lighting, security, fire control) and managed or owned by a completely different organisation that is not going to share their data.