WhatsApp now has at least 600 million active users, the company's CEO Jan Koum tweeted on Sunday, which should make Facebook very happy. Back in February, Facebook raised some eyebrows when it bought WhatsApp for $19 billion — far more than the $1 billion it paid for Instagram in 2012. Now WhatsApp, a mobile messaging service, is dominating the global competition, including China's WeChat, which counts 438 million active users. Another reason WhatsApp's numbers could have Facebook execs smiling? The company's standalone Facebook Messenger app didn't exactly garner rave reviews when it was released earlier this month.
— Keith Wagstaff