WhatsApp has 1.5 billion monthly users, but no obvious business model. Its founders were opposed to carrying advertising, and Facebook dropped a $0.99-per-year subscription fee when it bought the company.

“Acton and Koum acquiesced enabling Facebook to recommend that users’ WhatsApp contacts become their Facebook friends, allowing Facebook to collect more data about those relationships,” the Post reported. “The changes also allowed advertisers to feed lists of phone numbers into Facebook’s advertising system, known as custom audiences, and find new people to target with ads.”

Koum also plans to step down from Facebook’s board. His decision reportedly predates the company’s devastating Cambridge Analytica scandal, but reflects many of the same criticisms that have dogged Facebook in recent months. Zuckerberg wished Koum well on Facebook.

Since Acton left Facebook in September, he has become one of the company’s biggest critics, promoting #DeleteFacebook on social media and becoming executive chairman at Signal, a rival messaging app that emphasizes security and privacy.

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