I use to do this prank on my brother an he never new what to do so take a look and make your own stupid message windows.
Step 1. Open up notepad
Step 2. Type
lol=msgbox("Whatever you want message to say",20,"Whatever you want the window to be titled")
Ex:
lol=msgbox("Warning your computer has been infected by a virus ",20,"Virus Alert")
Step 3. Save the txt as .vbs extension
The number 20 represents the type of window style the message will be in. You can experiment with different styles you want.
-OdrAp