A pretty severe exploit known as Stagefright was uncovered some time back. Since its discovery, manufacturers have been working quick to get their devices patched up. Several devices have already been patched up and you can now add two more to the list.
HTC is currently rolling out patches to their former flagships, the M7 and M8. Unfortunately, the updates do not bring an updated Android version nor do they bring any other real software improvements. These updates are strictly to patch the Stagefright which is still reason enough to run the update.
The update should be hitting devices here regardless of carrier so if you haven’t received a notification yet, be sure to jump into the settings and do a manual check.