Apple has quietly released iOS 6.1.3 to fix a bug that could enable someone to bypass an iPhone’s passcode and access the Phone app. The only other change — beyond a variety of security fixes — is noted merely as “improvements to Maps in Japan.” The passcode bypass bug would allow someone with access to the iPhone to make calls, browse contact information, and access photos — it became public over a month ago.
The update is available for all iOS devices running iOS 6, including the iPhone 3GS and later, the iPad 2 and later, and the fourth-generation iPod touch and later. As always, an over-the-air update accessed from Settings > General > Software Update on the device itself will be faster to download and install, though you can of course download and install via iTunes as well. The over-the-air version is only 18.2 MB for my iPhone 5.
Since none of the security-related bugs fixed are all that serious, unless you’re relying on Maps in Japan, I suggest that you hold off on this update until others have determined whether or not it introduces any new problems.
One additional warning. Since one of the security holes closed by iOS 6.1.3 was relied upon by the evasi0n jailbreak, if you wish to jailbreak your iOS device, don’t upgrade. Of course, that also leaves you open to the passcode bug, but that’s one of the tradeoffs of a jailbroken world.