iPhone users instructed to take immediate action to avoid data breach: 'Urgent threat' Kurt 'The CyberGuy' Knutsson discusses Elon Musk's possible priorities as he exits his role with the White House and explains the urgent warning for iPhone users to update devices following a 'massive security gap.' NEW You can now listen to Fox News articles! The Apple iPhone is the most popular smartphone in the United States and one of the most widely used devices in the world. An estimated 1.6 billion