Former product executive Peter Deng warned colleagues about the existential threat of mobile messaging apps moving into Facebook’s core space. In an October 2012 email, he called messaging rivals “the biggest threat to our product that I’ve ever seen in my 5 years here at Facebook; it’s bigger than G+, and we’re all terrified,” he wrote, referring to Google’s now-defunct social media competitor. “These guys actually have a credible strategy: start with the most intimate social graph (i.e. The ones you message on mobile), and build from there.” Deng testifies he was referring to the three mobile apps that had started adding such features, and not the one Facebook ultimately acquired: WhatsApp.