Users do not use public Wi Fi.
Block unknown numbers.
Using your Wi Fi change the password of your router frequently.
You can lock Whatsapp message in Step. This is used by the third party app. Lock Whatsapp the name of the app can be downloaded from Google. A version of this app is also available for BlackBerry users.
You can hide the last scene. You will find many privacy settings in the phone from the taking of photographs until the last scene of hide.
To hide it youll go as SettingsAccount Privacy and then go to options in the last scene. Here you find such option like Everyone, My contacts, Nobody. Clicking on nobody of these in the last scene you will be completely Hide. This would be better than that do not share your number with others. So everyone used Whatsapp very carefully.