WhatsApp, the world’s most popular instant-message app with more than 1 billion users, is now fully encrypted on all platforms: Android, iPhone, Blackberry and others.

That’s good news for users who care about security and privacy, including journalists and dissidents. At the same time, it represents the intensification of a trend toward ubiquitous encryption that has posed challenges for law enforcement in the United States and around the world.

“The idea is simple: when you send a message, the only person who can read it is the person or group chat that you send that message to. No one can see inside that message. Not cybercriminals. Not hackers. Not oppressive regimes. Not even us,” WhatsApp co-founders Jan Koum and Brian Acton wrote in a blog post Tuesday.

Such encryption, in which only the sender and receiver can decrypt messages, makes it virtually impossible for foreign governments and U.S. agencies to intercept instant messages and voice calls, even with a warrant.