Anyone can call you on FaceTime and hear audio or see a video from your phone before answering. This bug has become viral on social media and the only protection is to disable FaceTime.
Update: Apple has now FaceTime disabled group on the server side. However, this may not have solved the problem. We always recommend to disable FaceTime until the problem is solved.
We learned this from 9to5Mac. In summary, all you have to do is make a FaceTime call. While the call is in progress, swipe from the top to the top, tap "Add Person" and add your own phone number. A FaceTime group call starts and includes the other person, even if they have not yet responded. Looks like they answered, but the call still rings on their lock screen.
All you can do is disable FaceTime to prevent people from monitoring you. If you see a FaceTime request on your phone, it is possible that someone is listening to you. From what we know, there is no way to limit FaceTime to your friends.
Apple said BuzzFeed News this "is aware of this problem and we have identified a patch that will be released in a software update later this week."
This is completely crazy. A bug of this size should be corrected immediately. Apple should close FaceTime to everyone if that's what it takes.
– Benji Mobb ™ (@BmManski) January 28, 2019
Since Apple does not address this issue with sufficient urgency, we recommend that you disable FaceTime for the moment.
On an iPhone or iPad, go to Settings> FaceTime and turn off FaceTime. You will need to repeat this process on all your devices, for example if you have both an iPhone and an iPad.
To disable FaceTime on a Mac, open the FaceTime app and select FaceTime> Disable FaceTime. You will also need to repeat this step on all your Macs.