Facebook announced this week that Facebook Messenger, its standalone messaging client that was first deployed in 2011, hit a new major milestone. The service is now used by 500 million people around the globe. That would be a pretty huge figure if not for one major problem: Facebook forced its users to download Facebook Messenger instead of using the now defunct in-app version. It’s still impressive, however, considering that WhatsApp, which Facebook paid about $19 billion to acquire, had 600 million monthly active users back in August.