[windows] What is %0|%0 and how does it work?

If you run a .bat or .cmd file with %0|%0 inside, your computer starts to use a lot of memory and after several minutes, is restarted. Why does this code block your Windows? And what does this code programmatically do? Could it be considered a "bug"?

This question is related to windows command-line

The answer is


It's a logic bomb, it keeps recreating itself and takes up all your CPU resources. It overloads your computer with too many processes and it forces it to shut down. If you make a batch file with this in it and start it you can end it using taskmgr. You have to do this pretty quickly or your computer will be too slow to do anything.


What it is:

%0|%0 is a fork bomb. It will spawn another process using a pipe | which runs a copy of the same program asynchronously. This hogs the CPU and memory, slowing down the system to a near-halt (or even crash the system).

How this works:

%0 refers to the command used to run the current program. For example, script.bat

A pipe | symbol will make the output or result of the first command sequence as the input for the second command sequence. In the case of a fork bomb, there is no output, so it will simply run the second command sequence without any input.

Expanding the example, %0|%0 could mean script.bat|script.bat. This runs itself again, but also creating another process to run the same program again (with no input).


This is known as a fork bomb. It keeps splitting itself until there is no option but to restart the system. http://en.wikipedia.org/wiki/Fork_bomb