Popular messaging service WhatsApp has reached 600 million monthly active users, according to the company's CEO, Jan Koum.
WhatsApp was approaching the half-billion user mark when Facebook agreed to buy the company for $19 billion in February, and passed that figure in April.
WhatsApp is one of a variety of SMS alternatives that allow users to send mobile photos and messages to each other via the Internet. Line, a app popular in Asia, has 400 million users and Facebook’s own Messenger service has 200 million.
Facebook’s purchase of WhatsApp is expected to be completed by the end of the year.