Apple later disabled the Group FaceTime feature while it worked to fix the ongoing issue.
Until Apple releases the patch, the best fix is to disable FaceTime on all your devices. This is how it works: you video call another iPhone user via FaceTime, then swipe up to open the menu options before the call has been answered.
The bug appears to be present on iPhones and iPads running iOS 12.1, and Apple PCs running macOS Mojave. If you speak, then the other person can hear you and hold a conversation, but this could be used to maliciously listen in to someone's iPhone without their knowledge.
The bug will also broadcast video if the recipient hits the power or volume button to ignore the call.
The incident is embarrassing for the technology giant as it was discovered on Data Privacy Day in the United States, which Apple chief executive Tim Cook had tweeted about, calling for "vital privacy protections".
As far as security flaws go, this one is particularly serious, especially given the emphasis has Apple placed on privacy recently when it comes to its devices and operating systems.
NY governor Andrew Cuomo issued a consumer alert for the product. "In New York, we take consumer rights very seriously and I am deeply concerned by this irresponsible bug that can be exploited for unscrupulous purposes", said Governor Cuomo. However, after two months of a successful run, the Group FaceTime feature caught a bug and had to be pulled down again.
The timing of the revelations about the bug is awkward for Apple, which is due to announce its latest earning report on Tuesday.