This happened by mistake once. OpenVMS allowed for command shortening vs completion so you could type h edit if you wanted help on the edit command instead of

This happened by mistake once. OpenVMS allowed for command shortening vs completion so you could type h edit if you wanted help on the edit command instead of help edit. One OS update broke that logic and h became halt. The results were unpleasant for many especially given OpenVMS at the time was commonly used on many financial systems, telco systems, government systems and much more. It's been a while so I forgot exactly when this happened but those impacted won't forget the experience.