You may be unable to access your Secure Box messages with your HTC One M7. HTC One M7 no longer supports Secure Box in the Messages application. To access Secure Box messages you will need to install a special .APK that will move the messages from Secure Box into the normal SMS conversation threads. These messages will become viewable using Messages, Hangouts, or your preferred SMS application. Follow these steps to move your messages:

1. Navigate to Settings > Security.
2. Enable Unknown Sources.
3. Using a web browser on the phone, navigate to http://dl3.htc.com/application/MmsHotFix.apk. The APK will download directly to the phone.
4. Open the File Manager app and locate the newly downloaded MmsHotFix.apk, tap it to begin installation.
5. After installation, open the MmsHotFix application to begin moving messages stored in Secure Box to the regular messages folder.
6. When the transfer is complete and the messages have been transferred, uninstall the MmsHotFix application

NOTE: Secure Box messages are not backed up. If you have previously performed a factory reset, the messages will be lost and cannot be recovered.