The Latest Android Security update patches the Factory Rest Protection bypass bug which is publicized recently. The bug allowed you to factory reset a Nexus device without requiring the credentials of the Google account previously associated with the device to reboot it again.
Yesterday a video has come up to disable FRP on a Nexus device. Note this devie is running on the December Patch. So why was the video only published yesterday? Presumably because Google disclosed the bug after it was fixed. Anyhow if your nexus device notify you for update do that to secure your device data from other persons (thief).
Did you people get the update on your phones? tell us what are your experiences and have even know about this bug yet?