In the six months since Facebook announced it was buying the messaging app, the service's monthly active user base has grown by 150 million.
It appears WhatsApp's popularity hasn't slowed since Facebook announced it was buying the service in February. The messaging app's CEO and founder Jan Koum posted on Twitter Sunday that the service now has 600 million monthly active users.
"Now serving 600,000,000 monthly active users. Yes, active and registered are very different types of numbers..." Koum tweeted.
WhatsApp is the maker of a 5-year-old mobile messaging app for exchanging texts, photos, and videos. The application is in the process of being purchased by Facebook for around $19 billion in cash and various stock options. The proposed deal has been approved by the Federal Trade Commission, but Facebook still needs to get international regulatory approval before it can complete the purchase.
In April, WhatsApp announced it reached the half a billion users milestone and that people share 700 million photos and 100 million videos on the app on a daily basis. At the time of Facebook's buyout announcement, WhatsApp had about 450 million monthly active users.
At $1 a year, WhatsApp is a cheaper alternative to SMS for those users in emerging markets, and appears to be already growing Facebook's total audience beyond the 1.23 billion people using the social network -- though it's unclear just how many people use both apps.