I would block access to the site via firewall. That is going to be your best-practice in this case.

If that isn't an option, though, why not write the script in native AutoIt scripting, then compile the script. It supports looping. You can also "hide" the AutoIt icon from the system tray (but not from Task Manager). I'm just wondering how you would get it to close gracefully when the user shuts their system down.