Some of my friends are big fans of WhatsApp, and have noted that I don't (and won't) use it, so I just wanted to briefly provide the major reasons why:
  1. It's owned by Facebook (and connected to the Facebook platform) and there are some major privacy concerns
  2. Since acquisition by Facebook, there have been major security concerns
Due to similar problems, I advise against using similar apps like Apple iMessage, Google Hangouts, Facebook Messenger, Telegram, etc.

If you're really keen on using a "Whatsapp-style" secure messaging app (with group messaging, voice calls, etc.), there is an alternative that is free, open source, and run by a non-profit organization.

It's called Signal and can be found at: 

I have it installed, so feel free to send me a test message to try it out, and let me know if you have any further questions about the various privacy and security concerns with some of these other messaging apps.

Further reading: