WhatsApp CEO and Founder Jan Koum has recently tweeted that WhatsApp active users count reached a milestone figure of 600 million users a month. Koum tweeted, “Now serving 600,000,000 monthly active users. Yes, active and registered are very different types of numbers.”

The mobile messaging app was developed 5 years ago to enables users to exchange texts, photos, and videos. Social networking site Facebook is in the process of acquiring the operations of WhatsApp at a price of nearly USD19 billion in cash and various stock options. The Federal Trade Commission has already granted approval to the proposal, but international regulatory approval is still pending before Facebook can complete the purchase.

WhatsApp announced in April 2014 that it has reached the half a billion users mark, with the users sharing 700 million photos and 100 million videos on the app on a daily basis. WhatsApp had nearly 450 million monthly active users when Facebook announced to purchase the app.

At a price of USD1 annually, WhatsApp is a much cheaper alternative as compared to SMS for users who are residing in the emerging markets. This is one of the reasons behind the continuous increasing popularity of the app.