With the release of iOS 9.3.1, Apple has stopped signing code for iOS 9.2.1, notes AppleInsider. This means users can no longer downgrade to the older version of operating system.
iOS 9.3.1 fixes a glitch in which apps (and sometimes iOS itself) would crash or hang when links were tapped. iOS 9.3 also featured an Activation Lock bug that affected older devices, including the iPad Air and earlier and iPhone 5s and earlier. It’s available to download through Software Update or at iTunes.
AppleInsider also notes that Apple has addressed customer concerns over a recently discovered iOS bug, noting an exploit that leveraged Siri and 3D Touch to gain unauthorized access to a user's Contacts and Photos has been fixed. However, the apparent server-side Siri update now requires a passcode or Touch ID authentication to search Twitter.