The .NET Developer's Guide to Windows Security

Chapter 4. What Is the Principle of Least Privilege?

The principle of least privilege was originally defined by Saltzer (1975):

Every program and every user of the system should operate using the least set of privileges necessary to complete the job. Primarily, this principle limits the damage that can result from an accident or error. It also reduces the number of potential interactions among privileged programs to the minimum for correct operation, so that unintentional, unwanted, or improper uses of privilege are less likely to occur. . .

I sometimes like to think about this principle in reverse. Imagine if you ignore it entirely and run all your code with full privileges all the time. You've basically turned off a whole raft of security features ...