Sam Gustin, writing for Motherboard: Facebook's decision to begin harvesting data from its popular WhatsApp messaging service provoked a social media uproar on Thursday, and prompted leading privacy advocates to prepare a federal complaint accusing the tech titan of violating US law. On Thursday morning, WhatsApp, which for years has dined out on its reputation for privacy and security, announced that it would begin sharing user phone numbers with its Menlo Park-based parent company in an effort "to improve your Facebook ads and products experiences." Consumer privacy advocates denounced the move as a betrayal of WhatsApp's one billion users -- users who had been assured by the two companies that "nothing would change" about the messaging service's privacy practices after Facebook snapped up the startup for a whopping $19 billion in 2014. "WhatsApp users should be shocked and upset," Claire Gartland, Consumer Protection Counsel at the Electronic Privacy Information Center, a leading US consumer advocacy group, told Motherboard. "WhatsApp obtained one billion users by promising that it would protect user privacy. Both Facebook and WhatsApp made very public promises that the companies would maintain a separation. Those were the key selling points of the deal."