LAST JULY, FACEBOOK CEO Mark Zuckerberg, along with the heads of Google, Amazon, and Apple, spent a long day fielding heated questions from members of the House Antitrust Subcommittee. Did he realize at the time that the most immediate threat to his company's business model would come not from Congress, but from one of the other executives at the hearing? If he didn't then, he does now. On Thursday morning, Apple CEO Tim Cook gave a speech explaining his company's upcoming privacy changes, which will ban apps from sharing iPhone user behavior with third parties unless users give explicit consent. And he made plain that these new policies were designed at least in part with Facebook in mind. Speaking as part of a conference convened for International Data Privacy Day, Cook excoriated the social media business model, which is based on monitoring people's behavior in order to target ads to them.