Suddenly after 3 months of purchase of my smart phone Moto G4 Plus, on 18 Dec 2016, Kaspersky antivirus for the phone started displaying messages that Realtime protection for the device is not available due to denial of access to Storage and Contacts; and WhatsApp also could not download photos, pictures, videos etc., with the same problem. Tried hard, but each time was faced with the messge "Screen Overlay Detected"bla bla bla. Finally, today one of the reviews in AndroidPit suggested to disable some mischief making Apps like CM Cleaner. CM Locker was installed on my device. Uninstalling the same solved the problem. Thanks.