Following the release of iOS 9.0.2 last week, Apple on Thursday stopped signing code for iOS 9.1 on compatible devices, prohibiting users from downgrading to the older operating system version.
As has become routine, Apple stopped signing for iOS 9.0.2 to ensure device owners are running the most up to date, stable code available, which translates to iOS 9.1.
Aside from stability improvements and fixes for bugs discovered in iOS 9.0.2, the latest iOS update released last week included a number of additional features. Owners of Apple's new iPhone 6s and 6s Plus, for example, receive a Live Photos enhancement that automatically senses when the handset is being raised or lowered to avoid recording unwanted movement. Also included is a list of more than 150 new emoji with support for Unicode 7.0 and 8.0 characters.
By ceasing iOS 9.0.2 code signing, Apple is effectively blocking users from taking advantage of a recent Pangu jailbreak release. The exploit used by Pangu's installer was patched in iOS 9.2.