The strong encryption makes it impossible for the company to comply with government demands for data. And since ProtonMail and its servers are located in Switzerland, there's nothing that US authorities can do to shut it down. The company gained a lot of publicity, much of it bad, when a leaked document revealed the app was a preferred choice for ISIS terrorists. "Unfortunately, technology does not distinguish between good and bad, so the same technology that protects democracy activists and dissidents can unfortunately also protect terrorists," it said at the time. ProtonMail also spearheaded a petition that successfully forced a public referendum on proposed Swiss privacy laws.