All iPhone owners should update to the latest version of iOS (9.3.5) immediately.
This patch addresses 3 recently identified zero-day exploits which apple has coined "Trident" . These exploits can be used to take control of your device and access your personal or business data.
If you’re unsure what version you’re running, you can check it yourself by opening the settings app and tapping General > About > Version.
Users should (as always) not open/download anything unless certain it comes from a trusted source. If uncertain, users should not click on any links without contacting their IT professional for assistance in determining if the item represents a security threat.