Mountain View is home to WhatsApp, an online messaging service now owned by tech giant Facebook, that has grown into one of the world’s most important applications. More than a billion people trade messages, make phone calls, send photos, and swap videos using the service. This means that only Facebook itself runs a larger self-contained communications network. And today, the enigmatic founders of WhatsApp, Brian Acton and Jan Koum, together with a high-minded coder and cryptographer who goes by the pseudonym Moxie Marlinspike, revealed that the company has added end-to-end encryption to every form of communication on its service.