The iOS 12.1.4 update will be available on all eligible devices over-the-air in the Settings app. To access the update, go to Settings --> General --> Software Update. Apple typically releases new iOS software at 10:00 a.m. Pacific Time or 1:00 p.m. Eastern Time, so that's when the update should become available.
With this update, Apple is fixing an insidious FaceTime bug that could allow someone to spy on you without your permission or knowledge. By exploiting this bug, someone could force a FaceTime call with you, giving them access to your iPhone, iPad, or Mac's audio or video even without you accepting the FaceTime call.
To do this, all someone needed to do was initiate a FaceTime call with you and then add their own phone number to the FaceTime call to convert it to a Group FaceTime call, which, apparently, forces a FaceTime connection.
From there, the person would be able to hear your audio, even though on your end, it would look like the call hadn't been accepted. If you hit the power button to make the call go away, it would give the person access to your camera.
In our testing, the bug was able to be initiated on iPhones running both iOS 12.2 and iOS 12.1.3, and it affected iPhones, Macs, and iPads running the latest version of Apple's software.
Shortly after the bug was publicized last Monday, Apple said that it was aware of the issue and was already working on a fix set to be released later in the week, which was later delayed until this week. Apple also temporarily made Group FaceTime unavailable by taking the server offline, which put a stop to the bug. Going forward, Group FaceTime will only be available on devices running iOS 12.1.4 or later.
With today's update, the FaceTime bug will no longer be able to be exploited, though it remains unclear if it has been available for use since Group FaceTime launched in October last year or if it became an issue in a later software update.