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When Facebook bought WhatsApp two years ago, the swallowed-up messaging company said in a blog post that "respect for your privacy is coded into our DNA". The app didn't ask your real name, email address or home address. But they never said anything about sharing your phone number.

In a new blog post today, WhatsApp announced it is changing the terms its privacy policy "as part of our plans to test ways for people to communicate with businesses". Among the changes, WhatsApp will allow its parent company Facebook access to its more than one billion users' phone numbers. The change "means Facebook can offer better friend suggestions by mapping users' social connections across the two services, and deliver more relevant ads on the social network," the Verge reports.

If you don't want Facebook to have your number, the good news is, existing users have a 30-day window to opt out of allowing Facebook access to their phone numbers once the update rolls out. By going to "settings" and then "account," within the app, you can change your preferences. As VentureBeat reports, instead of blindly accepting the terms and conditions agreement when you update the app, "you have to click 'read'. There you will see a control at the bottom of the screen inviting you to 'uncheck' the box giving your permission."

Here's what it looks like: