WhatsApp has just changed its terms of service to allow it to share user data with parent company Facebook for ads targeting. This is alarming as WhatsApp has committed to keeping user information separate when the company was bought.
If you did not pay attention and accepted those new terms, you can still opt out within 30 days by going to Settings tab > Account. There you will find a “share my account info” switch that you can revoke your permission.
WhatsApp has a FAQ page if you need more info.