WhatsApp has begun encrypting all its data by default, a decision that is likely to have a more significant impact on people and governments outside the United States. (Stan Honda/AFP/Getty Images)

WhatsApp, the world’s most popular instant-messaging platform, has begun encrypting all its data by default, a move that privacy advocates say will aid dissidents and human rights activists seeking to protect their communications from governments and hackers alike.

Open Whisper Systems, a group of software developers, said Tuesday it had partnered with Silicon Valley’s WhatsApp to build in end-to-end encryption that will make it impossible for foreign governments and U.S. agencies to intercept text messages, even with a warrant.

The move follows announcements by Apple and Google that they are encrypting, by default, data stored on iPhones and Android devices.

Law enforcement officials have warned that such encryption hobbles legitimate investigations of criminal suspects, and FBI Director James Comey said recently that the “post-Snowden pendulum has swung too far,” referring to tech companies’ reactions to the revelations of widespread government surveillance by former National Security Agency contractor Edward Snowden.

WhatsApp’s decision is likely to have a more significant impact on people and governments overseas, analysts said, as most of its more than 600 million users are outside the United States. The company already has begun encrypting instant messages sent on Android devices, according to Open Whisper Systems.

“We have a ways to go until all mobile platforms are fully supported, but we are moving quickly towards a world where all WhatsApp users will get end-to-end encryption by default,” Open Whispers said in a blog post.

Moxie Marlinspike, a San Francisco-based technologist who founded Open Whisper Systems, said the group’s goal is to make simple the sometimes cumbersome process of ensuring that communications stay private.

“From celebrity nudes to Iranian dissidents, private communication is valuable for everyone,” said Marlinspike, who goes by a pseudonym.

Founded in 2009 by two former Yahoo employees and now owned by Facebook, WhatsApp is used on a wide range of mobile phones, including iPhones, Nokias, BlackBerrys and Windows Phones.

Open Whisper Systems received grants from the U.S. government, including from Radio Free Asia, and from a number of foundations to help the group develop the TextSecure encryption protocol. The encryption is open-source, free and available online.

Such tools align with a major goal of U.S. foreign policy, which is Internet freedom. In 2010, then-Secretary of State Hillary Rodham Clinton urged countries to respect privacy and speech rights online. Since then, the State Department has funded the creation of privacy tools, including encryption technology, to allow people to hide their communications from oppressive governments.

“Encryption is the single most important cybersecurity tool,” said Peter Swire, a former White House privacy official who teaches law at the Georgia Institute of Technology. “We can’t begin to have effective cybersecurity unless we have wider use of encryption.”

Andrew Weissmann, a former FBI general counsel who teaches at New York University School of Law, said network security issues are not the only consideration. “You also have law enforcement and national security issues,” he said at a panel sponsored by New America’s Open Technology Institute. “There’s no perfect solution.” The issue, he said, is, “how can each side minimize the risk?”