Apple releases iOS 9.2.1, this upgrade has bug fixes & security improvements.
Changes on iOS 9.2.1
• Bug Fixes.
• Fix for an issue that could prevent the completion of app installation when using an MDM server.
• Security Improvements.
The iOS update is available via OTA(OverTheAir) going into Settings > General > Software Update or using iTunes.
For more information about the security upgrades visit Apples website: https://support.apple.com/en-us/HT201222