The Windows screensaver file extension is .src, but they're really just .exe in disguise. You can set any .exe to your screensaver by changing the extension to .src and selecting it under personalization settings.

@RegalBeagle sounds like a great way to set up a ticking time bomb. i have not used a screen saver since windows xp, probably not much even then though. i guess because today it is modern to just hibernate the computer and there is little need to keep it running while you are not there.