Brace yourself for the adpocalypse.
Global messaging service Whatsapp has announced it will start sharing users' phone numbers with parent company Facebook.
That means WhatsApp users could soon start seeing more targeted ads on Facebook - although not on the messaging service itself.
The company announced the move in a blog post on Thursday, saying it would update terms and privacy conditions to include new features like encryption and calling.
"We want to explore ways for you to communicate with businesses that matter to you too, while still giving you an experience without third-party banner ads and spam," the company said.
It's a subtle, but significant shift for the service, which has long promised to safeguard the privacy of more than one billion users around the world, but is also trying to find ways to make money after it was bought for $21.8 billion.
More information on what is changing between the two services can be found here.
For those that don't want to go ahead, users will have a limited amount of time to opt out of sharing information with Facebook, but will have to check a box to do so.
The change is the first update to privacy settings since 2012 and comes two years after Facebook took over the company.
At the time, it pledged not to interfere with a longstanding promise by WhatsApp's co-founders to respect users' privacy and keep ads off its messaging platform.
One changes announced by the company follows through on previous hints by WhatsApp executives, who have said they're exploring ways for businesses to communicate with customers on WhatsApp. That could include using WhatsApp to provide receipts, confirm a reservation or update the status of a delivery.
Companies could also send marketing offers or messages about sales to individual customers, according to the new documents, which note that users will be able to control or block such messages. WhatsApp says it will continue to bar traditional display ads from its service.
"We do not want you to have a spammy experience," the company said.
We want to explore ways for you to communicate with businesses that matter to you too, while still giving you an experience without third-party banner ads and spam.
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Another change is potentially more controversial:
WhatsApp says it will begin "co-ordinating" accounts with Facebook by sharing WhatsApp users' mobile phone numbers and device information, such as the type of operating system and other smartphone characteristics.
The company says Facebook will employ the phone number internally to better identify WhatsApp users on Facebook, so it can recommend friends or show targeted advertising.
The ads would come through a Facebook program called "Custom Audiences," which lets a business upload lists of customers and phone numbers or other contact information the business has collected from warranty cards or other sources.
Facebook matches the list to users with the same information and shows them ads.
Facebook says it doesn't give out users' information to advertises.
We do not want you to have a spammy experience.
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WhatsApp phone numbers are valuable to Facebook. While the social network already has many phone numbers, it doesn't require users to provide them, and doesn't always have the most current number for everyone on Facebook.
But anyone on WhatsApp must provide a current phone number because that's how WhatsApp knows where to deliver messages.
The co-ordination of accounts may draw fire from privacy advocates. WhatsApp has long promised not to employ user data for advertising. Its acquisition by Facebook two years ago sparked complaints from activists who worried the new owner would start mining WhatsApp accounts.
Though both companies pledged WhatsApp would operate separately from its parent, the Federal Trade Commission warned them publicly, in a 2014 letter, against changing how they employ WhatsApp user data without users' consent.
WhatsApp says current users have up to 30 days to accept the new policy terms or stop using the service. Once they accept, they have 30 more days to opt out of sharing with Facebook.
Privacy groups have praised WhatsApp for building powerful encryption into its services, making it impossible for the company or anyone else to read users' messages. WhatsApp promises that encryption will remain, so neither WhatsApp nor Facebook would be able to use message content for advertising purposes.