Issue with iOS 12 has messages being merged accidentally and received by unintended recipients
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Over the weekend, we told you about a passcode glitch in iOS 12 that could allow an attacker to break into a locked iPhone and look at a user's contacts and photos. Now, a new and potentially embarrassing bug has been discovered that can send your messages and texts to unintended recipients. For example, you might send an explicit text to a sibling only to have the message sent to your mother instead.
If you are experiencing this issue, hopefully signing out of Apple ID for messages will end the problem. Others in the forum have called this a workaround, and are still imploring Apple to come up with a fix of its own.
"We are experiencing this problem with our family of four who share the same Apple ID, and I can't even text my husband independently right now, or vice versa. This is our primary way of communicating all the time. Our two kids now see all four family member's messaging history on their phones because it has all merged into one. What's really bizarre is I will put my husband's phone number into the text message and type a test message, I will send it and it will say it went to my daughter who has an entirely different phone number. This is really messed up. This is not good and could cause a member of the family to read something not intended for them. I do hope Apple realizes how serious and problematic this situation is and fixes it asap."-vdewitt, member, Apple Communities
source: Apple
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