Re: S IP mple gix
Well - that's simple to say. Way less simple to implement.
Even considerably locked down systems, such as some Federal Court electronic filing and case management system were breached via the monitoring tools used to maintain its uptime. [0] These are systems designed to handle court sealed documents, which is just about as close to "Top Secret" as you can get in the civilian side of the world.
I'm sure they did their due diligence. However, security is always a cat and mouse game and the crims only have to get lucky once and the company (or court) has to always get it right.
[0] - https://krebsonsecurity.com/2021/01/sealed-u-s-court-records-exposed-in-solarwinds-breach/