Apple has disabled the ability to make Group FaceTime calls following the discovery of a major flaw that allows users to listen to audio broadcasted from a recipient's device before they answered the call.
The Apple system status page shows that Apple disabled Group FaceTime shortly after the bug was discovered and publicized on Monday evening. Originally reported and demonstrated by 9to5Mac, the potential for damage before Apple forced the feature offline was massive. As 9to5Mac put it, "if your phone is ringing with an incoming FaceTime request, the person on the other end could be listening in."
In a statement to BuzzFeed News, Apple announced that it has generated a fix to the exploit and that it will be deployed to iOS users "later this week." Until said software update is distributed, there is no longer any risk of this exploit being utlized because of Group FaceTime being disabled, so your FaceTime calls are safe.
For users that need group video conversations on their iOS devices in the meantime, good alternatives include WhatsApp Messenger and Hangouts, with WhatsApp supporting up to four simultaneous video call participants and Google Hangouts supporting up to 25 participants.