Well ... I was working for a large multi-national running HP-UX systems and Oracle/SAP, and one day the clock struck twelve and the OS just started to disappear

Down went SAP and Oracle like a sack of spuds!
Mayhem broke with the IT manager standing over my shoulder wanting to know what had happened ... I did not have a clue, and I could not even get onto the system as it was completely hosed! So the task of restoring the server began and after 30 minutes I had everything backup and running again. phewww
Until 1pm! The system disappearing again

What the hell is going off, panic set it, this time I managed to keep a couple of sessions open to allow me to check the system.
And then it clicked .... I wonder .... Yep indeed, somebody had setup a cronjob AS ROOT, that attempted to 'cd' to a directory which then proceeded with a 'rm -rf *'

Though the ******* other admin did not verify that the directory existed before performing the remove! Well once we had restored the system again, the cronjob was removed, and we were all running fine again.
Morale of the story is to always protect root access and ensure you have adequate backups!!!