By David Meyer
August 25, 2016

At the start of this year, hints emerged that WhatsApp was about to start sharing user data with its parent, Facebook (fb). Well, that’s definitely going to happen now.

As changes to WhatsApp’s terms and privacy policy make clear, Facebook will now be able to access the user’s phone number and analytics information, such as the last time they used the service. Other shared information will include the user’s mobile operating system, screen resolution size, a device identifier, and a mobile country code.

WhatsApp said Facebook would be able to show people more relevant ads based on what the social network can glean from the WhatsApp data.

The sharing of phone numbers will also make a difference for people who have so far declined to tell Facebook their phone number or the email address they share with other people.

Let’s say someone named Peter has decided to remain private in this way. Jane, who knows Peter and has his contact details, joins Facebook and uploads her address book. But Facebook can’t suggest Peter as a friend because it doesn’t have the same details about him. With the two systems being linked, if Peter uses WhatsApp, then Facebook will now be able to suggest him as a friend to Jane.

However, existing users can opt out of having their data used in this way. When they are prompted to agree to WhatsApp’s new terms, they can click “read,” and at the bottom of the screen they will see a tick box about sharing WhatsApp information with Facebook.

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If you don’t want Facebook to use your WhatsApp information to target ads and make friend suggestions on the social network, untick the box and click “agree.”

If you clicked “agree” without unticking that box and regret your choice, you will have 30 days in which to untick the box through the WhatsApp settings menu. It’s only after that date that Facebook will start using the data in question.

However, unticking the box will only limit what Facebook does with that information. It won’t stop Facebook from linking WhatsApp and Facebook accounts.

This is bad news for those who like WhatsApp’s semi-anonymous nature—it doesn’t ask for users’ names or other personal information, whereas Facebook operates a real-name policy and heavily profiles its users.

The messaging app’s previous terms and conditions promised that it would not use the user’s phone number and personally identifiable information for commercial or marketing purposes without their consent.

Although users can limit what Facebook does with their data, the mechanism for doing so is less than obvious and doesn’t stop the data going to Facebook. WhatsApp chief Jan Koum’s promises about maintaining the service’s pro-privacy policies, made back at the time of the 2014 acquisition, are being stretched to their limit.

Privacy advocates are, unsurprisingly, not pleased about WhatsApp’s decision to use customer data for profiling purposes.

In a Q&A, WhatsApp said the data-sharing would help it to more accurately count unique users and fight spam. For example, if someone is sending out spammy links on Facebook, the new link could help WhatsApp crack down on the same user.

The messaging outfit stressed that Facebook would not show users’ phone numbers to their contacts. Facebook also won’t get to read the contents of WhatsApp messages—the nature of their end-to-end encryption means no-one but the sender and recipient can read them.

For more on WhatsApp’s encryption, watch:

As Facebook and WhatsApp have previously indicated, the plan is to integrate business-to-consumer communications into WhatsApp. This will help monetize the service, which stopped charging subscription fees earlier this year.

The new terms and privacy policy also make this possible. WhatsApp said it would test features in the coming months, such as messages from banks about potentially fraudulent transactions, or from airlines about delayed flights.

WhatsApp is adamant that, although its changes will improve the targeting of ads on Facebook, the messaging service itself will remain free from “third-party banner ads and spam.”

“We do not want you to have a spammy experience; as with all of your messages, you can manage these communications, and we will honor the choices you make,” Whatsapp said in the Q&A.

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