If you know they are there then manage the network and environment to limit the risk.
What's being discussed here are undocumented network connections that were wired to the primary controls through a secondary data bus so that standard monitoring tools wouldn't see the traffic.
Even if it isn't malicious it's terrible, no-good, shitty design work.
https://cybersecuritynews.com/u-s-officials-investigating-rogue-communication-devices/
So I read the whole article and the acquittal happened because German Police did not translate the section informing the person what they were being accused of. That's no small thing.
Then there's the fact that the German Police kept turning off the recording during the interrogation, there's no mention of "homicide" on the recordings, and you can't hear the accused voice on the recordings!
So basically there's no proof that the accused knew what he was charged with nor is there any direct recordings of his confession.
The only thing this shit proves is that German Cops are as bad at their fucking jobs as American Cops.