For months, the company had been tracking WhatsApp obsessively using Onavo, a VPN and data analytics app, whose data showed that the messaging app was not just a rising competitor, but a potential Facebook killer. Now, newly published confidential Facebook emails and charts show exactly why CEO Mark Zuckerberg spent a small fortune for the messaging app. The acquisition price was staggering for an app that made little money and was largely popular outside the United States. In February 2014, Facebook purchased the messaging service WhatsApp for $19 billion.
