The iOS 10.3.3 update addresses vulnerabilities with your Contacts, Messages, Notifications, Safari and other issues. One of the more potentially damaging exploits was hidden in the iPhone's Wi-Fi chipset, where an attacker could take over a device remotely if it was searching for a signal.
For this Wi-Fi-based attack, you'll want to upgrade. If your iOS device has its Wi-Fi turned on, attackers in range could find your device, remotely take over its Wi-Fi chip and crash your phone.
This is the Broadpwn exploit, which Google patched for Android devices on July 5, listing it as a critical security flaw. It affected a broad range of devices from companies like HTC, LG and Samsung. The attack doesn't need your device's PIN or password to exploit the weakness.