It is a safe prank using command prompt and batch files. It is easy and fun to learn.
I am not held responsible for any problems this may cause to your computer making this or distributing it to your friends.
Nor responsible for injury from un-happy friends upon receiving this.
Just incase you aren't able to view the video, here is the direct link. (The video is unlisted thats why I gave a direct link.)
EDIT in the video when i say less than its supposed to be greater than. The symbol is correct but not what I said.