In computer terms, to fork a program means that a running program of some sort makes a copy of itself and keeps running. Usually this is managed so that the computer is not overwhelmed, and eventually the forking process and its children exit in some fashion. However, poor management or malicious intentions can cause an infinite chain reaction. This is known as a fork bomb.

The easiest way to make a fork bomb is make a program with an endless loop that calls the fork() system call (or something similar). My favorite fork bomb for UNIX has a payload. This will only work if the victim has a properly configured command line mail client:

This is written in Perl and sends constant requests to The Internet Oracle.

Note: DON'T DO THIS