When Fernando Corbató accepted the Turning Award for, among other things, inventing the computer password, he described my new favorite bug.

From On building systems that will fail (1991), by Fernando J. Corbató

  1. Imagine a UNIX system with one admin user.
  2. The system grows, and the single admin user become a bottleneck. So it’s decided that multiple people can log into the admin user at the same time.
  3. A certain (unnamed) text editor is used to edit files. This text editor assumes that only one instance of it will be open at a time.
  4. One person is logged in as admin, and starts editing the system password file.
  5. Another person is logged in as admin, and starts editing the message of the day file.
  6. One ill-timed save file later, and the system password file is saved as the message of the day.