Facebook's WhatsApp has begun alerting its 2 billion users to an update of its privacy policy -- and if they want to keep using the popular messaging app, they have to accept it. The new terms, delivered in early 2021, have caused an outcry among technology experts, privacy advocates, billionaire entrepreneurs and government organizations and triggered a wave of defections to rival services. WhatsApp says the change is necessary to help it integrate better with other Facebook products.