A Washington Post interview with a friend of Jack Teixeira, the 21-year-old US Air National Guardsman suspected of leaking a trove of highly sensitive documents, has brought to light the nature of their group on Discord, a online messaging platform. It's far from the first time a gaming forum has been the source of a military leak. Technology Editor Peter O'Brien takes us back over some other famous examples of leaks and explains why they're the perfect environment for such breaches.