The sysadm caught him playing it and promptly unistalled the game.
However the important business application hosted on the server then stopped working and no one could figure out why.
Nothing would work... even after lots of debugging, error log analysis and redeploying.
The developer suggested installing Doom again and lo and behold, the application started working.
Software would ship with shared DLL's, uninstalling an application would usually have a knock on effect.
MS-DOS was used a lot for small office servers. Whilst Windows NT4 was growing in popularity, it was an expensive option for firms. Plus it was hard to play games on NT4 due to memory protection issues.
A fable of Doom being needed to run a server in today's environment is ridiculous, however back then things were a lot less mature. The issue wasn't limited to just games. Any application with shared files was a nightmare, normally you just renamed files, rebooted, then if things worked you could delete the files.