Open notepad and type this:
lol=msgbox ("Warning a virus has been detected on your PC. Press YES to format your hard disk now or press NO to format your hard disk after system reboot",20,"Warning")
Then save it as Virus.VBS
and go to the folder that contains it and open it if a window pops out saying a virus has been detected it's working. Press yes or no to close the window and put it in the startup folder of the victim's account.On startup the window should appear.Note: This does not harm your computer as it does not contain virus.