Imagine being ten years into the apocalypse and discovering your computers are infected by the NSA
Don't kid yourself. Their stuff runs on every machine out there according to Edward Snowden and both Apple and Microsoft have fully cooperated in seeing to their unrestrained access.
Will never happen with a version of DOS running your server and your clients running simple browsers. Don't hook up to the internet and your intranet will stay absolutely pure forever.
My book on Vault-OS will tell you a dozen tricks you can use to make your simple DOS network run ten times faster than anything you have ever seen. Once you get rid of all that spook overhead you would be amazed at just how fast TCP-IP is.