Originally Posted by rickair7777

I was not suggesting that would be a practical COA for a bad actor...it would take too much knowledge of too many systems and there are too many people who might notice. But as an academic exercise you could probably demonstrate something along these lines with enough resources.

I have relevant education and civilian and military experience on this. Lets just say the military bit is particularly relevant here. Like I said the only limitation is hardware, access, and skill. Firmware may be an access problem in some cases but even firmware has been re-written remotely. It depends on the design, but for example most consumer electronics can have their firmware updated via the internet...you don't need a tech with a dedicated physical connection.

Without getting too far into the weeds, it would be hard to update firmware in flight because it would take the device offline for at least a while. But if it were modified on the ground with the intent of being used later in flight...

It's a bit of a stretch that an airplane could be sent off course for long with no one noticing, the point being that you could make a real mess of things.

This is all limited by access and the available skillset. But do not underestimate the creativity of people who spend all their time contemplating these things. It's too late to make our systems tamper-proof (probably no such thing anyway) but it would be a good idea to limit access to the degree practical.

The real threat is probably economic disruption caused by a state actor in time of low-intensity conflict.