Don’t be too worried though, the update only allows WhatsApp to share your basic information with Facebook, and will not be made public. The information shared includes your phone number, profile name and photo, online status and status message, and last seen status. The content of your message will not be shared and will remain encrypted with end-to-end encryption. Facebook stresses that
“Your encrypted messages stay private and no one else can read them. Not WhatsApp, not Facebook, nor anyone else. We won’t post or share your WhatsApp number with others, including Facebook, and we still won’t sell, share or give your phone number to advertisers.”
Make sure you tap on the “Read” link
And uncheck the option to share information with Facebook
If you’ve already clicked on “Agree” without reading, you can still change it (only 30 days to do so). Just go to Settings, and under Account, uncheck “Share my account info”.