lol these are really lame beginner's programmer's pranks
most intermediate users can see through them

a friend of mine did this at school to fool the sysop and it actually worked:

1. Get some kind of error message that actually exists, for example something.exe has stopped responding or something more fun
2. Press ALT+Printscreen
3. Go to paint, press CTRL-V
4. Save it as
5. Set it as wallpaper, be sure to select 'Center' from the dropdown box, and make sure theres no icons in front of it

The sysop literally tried clicking it away but it won't cause its just an image ha ha ha