A number of Windows Phone users have received a notification on their Windows Phones regarding the post-NoDo update that was to patch some security issues regarding certificates. The update OS version number is 7.0.7392.0.
For the most part, this is a fairly minor update and a non-issue for adding new features. It is solely to address some issues for fraudulent digital certificates. It might also include previous updates that were not installed, like the pre-update or NoDo.