Google has removed a feature of the Android operating system that has been used in the past in ransomware attacks. These are special “system”” windows that are shown above any app on the user’s screen. Google reclassified the permissions of these system windows to the “”Above dangerous”” class. This means ransomware authors will need to find new ways of showing ransom notes and locking users’ screens. Google is now allowing users to shut down apps that show other types of system windows. Google also added anti-ransomware improvements with Android O (8.0)”
Source: https://www.bleepingcomputer.com/news/security/android-o-will-contain-special-feature-to-fight-off-ransomware/