Messaging application WhatsApp is being used by one billion people, the company behind it has said.
The California-based firm announced the milestone just six years after it was founded by ex-Yahoo! employees Brian Acton and Jan Koum.
The app's popularity has stemmed from its allowing groups of people to stay in touch simultaneously without having to enter contact details.
As well as text messages, users can also share photos, videos and other media.
It also offers a similar secure messaging service to the BlackBerry and has become more popular as the Canadian phone maker has seen its handsets fall in popularity compared to those made by other smart phone makers.
It has also proved popular in the US where mobile phone customers often have to pay for text messages.
More than half of its subscribers have been added in the last 21 months, according to Forbes.
A message on the app's blog section said: "One billion people are using WhatsApp. That's nearly one in seven people on Earth.
"We are proud of this milestone, and we're humbled by the extraordinary ways all of you have used WhatsApp.
"WhatsApp began as a simple idea: ensuring that anyone could stay in touch with family and friends anywhere on the planet, without costs or gimmicks standing in the way.
"So even as we celebrate this achievement, our focus remains the same.
"Every day, our team continues to work to improve WhatsApp's speed, reliability, security and simplicity. We're excited to see how far we've come. But now, it's back to work – because we still have another 6 billion people to get on WhatsApp."
WhatsApp was bought by Facebook in February 2014 for $19bn (£12bn).
It is popular in India, which has the largest number of users for a country, but faces competition in Asia from other messaging services like WeChat and Viber.
The app has proved controversial in some countries where fears remain over secure messaging, with Brazil trying but failing to ban the service in December 2015.
But supporters point to its successes such as helping refugees avoid getting into difficulty while crossing the Mediterranean Sea.
