An illegal operation is a command a computer cannot execute or does not understand. The computer will return an error to the user, alerting her to the fact that it failed to execute a command, and the program a user is running may be terminated by the operating system. A number of things can cause an illegal operation. Usually people can resume normal activities after the error message displays, but sometimes the error may repeat, indicating a more serious problem and the need for troubleshooting.
Processors handle a number of commands at any given time, especially when people are running multiple programs. An illegal operation can occur when computers try to manage memory leaks or receive nonsensical commands from confused or overloaded programs. The processor will tell the operating system it could not complete an operation, and the operating system will generate an error message to tell the user. It may also inform the user that the program will be shut down.
When a program closes because of an illegal operation, the operating system will try to save data so when the user reopens it, he will suffer only minimal data loss. Sometimes this is not possible. Regularly saving and backing up data is a good idea to prevent catastrophic data loss as a result of a system error. If the program keeps encountering errors, something may have gone wrong with the installation, or it could be conflicting with another program, plugin, or driver.
If the illegal operation does not close the program, the user should save, take note of what was happening when the error occurred, and keep working. If more errors happen, it can be a sign that something is wrong. People should think about the most recent system changes. Something like upgrading software, changing drivers, installing a new peripheral device, or making other changes could create a conflict. It may be possible to roll the system back to address the problem. People can also look up system conflicts on the Internet to see if the issue is known.
Repeat illegal operation error messages when no apparent system change has been made may be a sign of a virus or a problem with the computer. A technical support representative can help the user work through some diagnostic tests to learn more about what is happening. It can be helpful to note down the details of the error message, including any error codes displayed.