If New Message Popup is enabled on your Android device, a popup opens when a new message is received. If you don't want to see the message preview on the popup window, do as follows on an LG Optimus G device:
1. Open Messaging application
2. Press the menu button and select Settings.
3. Go to Notification settings
4. Make sure to unmark "New Message Popup" to disable the feature
5. To disable previewing contents of received message, unamrk "Preview" too