The bug, which was recently discovered and been demonstrated on video here, can cause Messages to quit unexpectedly.
Apple is aware of an iMessage issue caused by a specific series of unicode characters and we will make a fix available in a software update. Until the update is available, you can use these steps to re-open the Messages app.
● Ask Siri to "read unread messages."
● Use Siri to reply to the malicious message. After you reply, you'll be able to open Messages again.
● In Messages, swipe left to delete the entire thread. Or tap and hold the malicious message, tap More, and delete the message from the thread.
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