Apple has responded by disabling the Group FaceTime feature, which is related to the bug, but that may not be enough. The only way to ensure nobody is listening to you is to answer every call (so you at least know that they are listening to you) or to disable the app.
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Sould Apple not just have Siri analyze useage and then in the future(when it is legal) send terminators back in time to punish those FaceTime users she judges to have abused this feature/defect for eavesdropping?