
iOS 9.3.5 is a major security update having to do with Israeli-based digital arms deal NSO Group. The group was usuing two kernal bugs to exploit the software, allowing for the tracking of emails, calls, location, and passwords.
Via New York Times:
"In interviews and manuals, the NSO Group’s executives have long boasted that their spyware worked like a “ghost,” tracking the moves and keystrokes of its targets, without leaving a trace. But until this month, it was not clear how exactly the group was monitoring its targets, or who exactly it was monitoring.
A clearer picture began to emerge on Aug. 10, when Ahmed Mansoor, a prominent human rights activist in the United Arab Emirates, who has been tracked by surveillance software several times, began receiving suspicious text messages. The messages purported to contain information about the torture of U.A.E. citizens."
This seems like a very important update for those worried about security. We must warn you that if you are Jailbroken or plan on Jailbreaking, the update should be avoided, as there is now Jailbreak for this firmware.