Google Hangouts app among Google Android users received spammy messages this week. Cybersecurity researcher Absss Abss identified Android apps that had been careless with their popup notification keys. He found a way to deliver rogue messages by making a specific request to the Firebase Cloud Messaging service interface based on what FCM calls topics. FCM allows a notification to be tagged for delivery to users who are interested in various combinations of topics, and this meant he could easily find a topic specifier that covered all users of any app.”]