What exactly does it fix? By googling I got to know that it fixes some bug related to the lock screen. Do any one know of that bug. Got to know regarding this as I got a notification regarding software update in the device.
The update is just a bug fix update, no new features. The lock screen bug that you mentioned allowed bypassing the lock screen for a short amount of time, details can be found for example on TheVerge or AndroidCentral.