As we all know, Whatsapp was acquired by Facebook in 2014 for a ransom of $19 billion. After the acquisition the CEO, Jan Koum came out point blank that Whatsapp will still work independently; meaning no invasion of privacy and no ads.
But by coordinating more with Facebook, we’ll be able to do things like track basic metrics about how often people use our services and better fight spam on WhatsApp. And by connecting your phone number with Facebook’s systems, Facebook can offer better friend suggestions and show you more relevant ads if you have an account with them
They have also stated clearly that your data remains private and they have no intention sharing your messages or phone number.
Nevertheless if you feel unsecured by this, you have the opportunity to opt out and here is how to do so. You have at least 29 days;
Go to SETTINGS >> ACCOUNT >> SHARE MY ACCOUNT INFO and uncheck the check box. With that you are out.