The new version appears to be rolling out in waves, and iOS device owners will at some point receive a notification that their devices are eligible for an update.
The update fixes an exploit activated by making and then immediately canceling an emergency call on a passcode-locked device. A malicious user with access to the device could use the exploit, plug the device into a computer via USB, and potentially access the data stored on the handset.
The new release of iOS comes nearly a month after Apple pushed out a beta build of 6.1.3 with a fix for the lockscreen bug.
The update also contains fixes for the Apple Maps application for Japan. Apple has been tweaking the Maps app for Japanese iDevice owners since February, focusing on pronunciation and other aspects of turn-by-turn navigation.
Apple also released version 5.2.1 of the firmware for Apple TV. The new version patches security flaws that could have allowed a local user to execute unsigned code or to execute arbitrary code in the kernel.