Apple released iOS 9.3.5 today for iPhone and iPad that patches a serious security vulnerability. I recommend installing it as soon as possible.
To download and install the patch, perform the following steps:
Go to Settings –> General –> Software Update and follow the prompts.
As with any update, please make sure you have at least 50% battery or plug in your device so you don’t lose power during the update process.
For more information on what triggered this patch, click the link below.
SOURCE: Citizen Lab