I've always found that servers are least vulnerable to attack when turned off, removed from all networked systems, or otherwise isolated from the world.
This is it. That's the full answer.
This answer is just rude and does not even try to be helpful so I flagged it as "Rude or abusive", which has the following explanation:
A reasonable person would find this content inappropriate for respectful discourse.
Naturally I was surprised to have the flag denied! I would like clarification from a diamond moderator regarding this. Some situations are obviously opinion-based, but I think this is a clear case of content that should be removed - it's even collecting upvotes, showing visitors that it is a relevant and useful answer!
If not "Rude or abusive", which flag should I have used?