“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. For example, you might see an ad from a company you already work with, rather than one from someone you’ve never heard of.”
This certainly goes against WhatsApp’s earlier assertion regarding its commitment to privacy.
You Can Opt Out
There are two methods of opting out of WhatsApp sharing your number with Facebook. The first has to be done before you accept the messaging app’s new terms of service. Rather than clicking “agree,” press the smaller “read more” option below, and uncheck the box that reads “Share my WhatsApp account information with Facebook…”
Even if you have already opted in, you still have 30 days to opt out.