The AT&T variant of the HTC One A9 smartphone will start receiving its December security update today. In fact, according to the information shared by HTC's Mo Versi on Twitter, the roll out should have already begun.
As mentioned by Versi in the tweet, aside from security fixes, the update also includes improvements to the camera. If you haven't received the update notification yet, you can also manually check for it by heading to your phone's settings.
For those who aren't in the know, the One A9 will also be getting the Android 6.0.1 Marshmallow update this month.