In computing, a fatal error or fatal exception error is an error that causes a program to abort and may therefore return the user to the operating system. When this happens, data that the program was processing may be lost. A fatal error is usually distinguished from a fatal system error (colloquially referred to by the error message it produces as a "blue screen of death"). A fatal error occurs typically in any of the following cases:

• An illegal instruction has been attempted
• Invalid data or code has been accessed
• An operation is not allowed in the current ring or CPU mode
• A program attempts to divide by zero. (Only for integers; with the IEEE floating point standard, this creates an infinity instead)