As part of WWF Australia's Earth Hour campaign we launched the world's only useful screensaver. Useful because it urges people to do something: turn off their computers when they don't need them. Downloadable from uselfulscreensaver.com.au, it displays messages reminding people that computers left on for no reason are a waste of energy and a source of greenhouse gas. Included in these messages are calculations of the time the computer's been left idle and how much energy's been wasted in this time. Exciting graphics are deliberately not part of the screensaver in case they tempt you to keep your computer switched on.