A free program for Android, by Prashant Bhoir.

Whatsup is an easy-to-use, time-saving app that allows you to securely send and receive text, audio, and video messages with your friends, family, and coworkers. Whatsup Chat Locker will let you send private messages that can only be read by the person you send them to. You can also choose to activate the screen that appears when someone sends you a message, which will prevent others from seeing what you’re doing at the moment. 

It’s easy to use: just tap the chat you want to send a message to, type in the person’s name, and tap “send.” If the person is not in your contacts, you’ll be able to search for them by typing their name in the search box. 

This app is ideal for:

You want to chat with a friend or family member who lives far away and doesn’t have access to the Internet. 

You want to send a photo or video message to a friend but don’t want them to be able to see it. 

You want to chat with someone you met on a website but don’t want to give them your phone number.