In iOS 7, Apple gives users an option that they’ve waited for a long time on iPhone or iPad. Notification Center, the place where we can find all notifications from iPhone and iPad applications, and displayed the most important information of the day, can finally be accessed from the lock screen, which means you will not have to unlock your device to see missed notifications. While this is a useful shortcut for all users, not just for those who have activated a lock code, it may be a privacy issue and security even as all notifications, messages, and the entire book can be viewed by anyone that grabs your device, without even having to type the lock code. If you think that this is not a problem for you because notifications are still displayed on the lock screen (option that can be disabled), then you might want to disable SMS or iMessage preview.
Disabling this option, your device will not display some of the message content in notifications, alerts, banners or notification center, so you can rest assured when you get a message that cannot be read by a curious friend as long as they don’t know the lock code or have your fingerprint.
How to disable messages preview in alerts, banners and notification center on iPhone or iPad:
Open setup application on the home screen of your iPhone or iPad
Reach Center notifications and configuration
Scroll to the Include section, and reach the Messages button;
In the opened page, run until the Preview option, where you can switch the button to gray (O).
From now on there will be no preview display on any messages received on your device. Instead, when you get a message, the notification will be displayed as the message type and subject (eg, “iMessage” and “SMS”).