If you haven’t updated your iPhones and iPads to iOS12.4.1, you should do immediately. The reason for this is that Apple’s recent iOS12.4 update actually reopened an old security flaw. Google’s Project Zero Team discovered the flaw. They report that it potentially allows a malicious application to take complete control of your iPhone.
The Guardian article “Apple accidentally reopens security flaw in latest iOS version” explains in more detail.