Instant messaging service WhatsApp has strengthened privacy for its more than one billion users
The Facebook-owned app announced Tuesday that it has added full end-to-end encryption for all communications. That means all text messages, file transfers and voice calls are scrambled en route between users' phones so they can't be intercepted.
"The desire to protect people's private communication is one of the core beliefs we have at WhatsApp, and for me, it's personal," said Jan Koum, one of the app's founders who was raised in Ukraine under Soviet rule.
"The fact that people couldn't speak freely is one of the reasons my family moved to the United States," he said in a statement.
WhatsApp started introducing end-to-end encryption in 2014, but it's taken until now to extend it to all communications across all devices. Users need to be using the latest version of the app to ensure they benefit from the measure, it said.
Amnesty International called WhatsApp's move a "huge victory" for free speech.
"Every day we see stories about sensitive records being improperly accessed or stolen. And if nothing is done, more of people's digital information and communication will be vulnerable to attack in the years to come," the WhatsApp statement said. "Fortunately, end-to-end encryption protects us from these vulnerabilities."
By bringing it to the entirety of its vast user base, WhatsApp has made the technology the most widely used cryptographic tool on the planet.
Encryption has become a hot-button issue around the globe. The feud between Apple and the FBI fueled a fierce debate over the tradeoff between individuals' privacy and the demands of law enforcement.
The U.S. Department of Justice asked the tech giant to unlock the iPhone of one of the terrorists involved in the San Bernardino shootings in December.
Apple refused the request and fought a court order ordering it to comply. The company said the demand would force it to create a "backdoor" that could potentially allow the government or hackers break into similar iPhones.
The FBI eventually dropped the case after it managed to get into the iPhone with the help of an unidentified third party. But Apple is opposing similar demands by U.S. federal law enforcement in at least a dozen other active cases.
WhatsApp filed an amicus brief in support of Apple's stance, as did several other major tech firms including Google.
The push to introduce end-to-end encryption has brought the app into conflict with law enforcement.
Brazilian authorities have demanded WhatsApp hand over IP addresses, customer information, geo-location data and messages related to an ongoing drug trafficking case.
WhatsApp says it has been cooperating, but is not able to provide "the full extent of the information law enforcement is looking for" because of the encryption it had already implemented.
A Brazilian judge ordered the service blocked countrywide in December after WhatsApp failed to respond to court orders. The ruling cut off all 100 million Brazilian WhatsApp users for 48 hours before a senior judge overturned it.