I'm late to the party, but I noticed something that begs a errata.
In the second edition open play test docs for mesh activities every device has it's very own micro AI defending it. Ok, I gather a simplification to just help things along, it also turns out to be a extra rule with a very bad loophole.
Get some motes, ectoes, or just arrange anything sing from least mission critical to most mission critical. Every firewall but the far end three rules. /Only/ three rules.
1. Only accepted incoming connections from the next up the line.
2. Only forward traffic to the next device down the line.
3. Discard all other traffic.
By this point you have to get by the entire party's line of device 4-20 (without artificially extending it), in order, without raising a single alarm. Doable, but difficult in your getting into odds that are 1% or lower.
Every 6seconds randomize the order in preset and compartmentalized ways. A compromised device might know the next device in the chain, but after that it has to guess. Every reset every device knows exactly where an intruder is. A device either violates one of the three rules when connecting to it out of order, or traffic to or from the device is sniffed that violates one of the three rules (Because the hacker doesn't know the new chain order).
Compromised devices in the chain can be instantly flagged, cut out, shutdown, restored from secure backups made before the mission starts, and put back into service. To compromise a network a intruder must now hack every device in a chain 4-20, they must do it every time, without fail, the first time, in under 6seconds.
Edit 2:I forgot cycling devices out of the chain to reset them (or pass updated chain orders along) even if not compromised to clear any rootkits or backdoor that slipped in.
Edit: Because of so many eyes under direct player control -that you can perfectly predict- hacking becomes statically impossible.