You might want turn off FaceTime right this second. There’s a nasty new bug in iOS 12 that lets FaceTime callers hear sound from the recipient’s microphone even if they haven’t picked up. It works by exploiting a bug with Apple’s newish Group FaceTime feature introduced in iOS 12.1, but fortunately Apple says a fix is already in the works.
Update 2/1: Apple has issued a statement apologizing for the bug and promising a fix next week.
In a media statement quickly after the story began spreading, Apple acknowledged the existence of the bug: “We’re aware of this issue and we have identified a fix that will be released in a software update later this week.” About an hour later, Apple disabled Group FaceTime altogether.