Puzzle of the Day

The UNIX operating system (and most computer systems) have an all-powerful user (root or operator or wheel).

1.	Why does such a user exist?

2.	Dennis Ritchie called the existance of this user "both a theoretical and practical flaw." Why?

3.	If you were designing an operating system with security being a key goal, could you avoid creating such a user? 
If so how? If not, how would you implement the functionality of the root user?