http://time.com/5515517/apple-fixing-facetime-bug/

Apple has disabled a group-chat function in FaceTime after users said a software bug could let callers activate another person’s microphone remotely.

With the bug, a FaceTime user calling another iPhone, iPad or Mac computer could hear audio — even if the receiver did not accept the call. The bug is triggered when callers add themselves to the same call to launch a group chat. That makes FaceTime think the receiver had accepted the chat.