The issue first gained attention on Reddit earlier today. The string of text is a series of Arabic characters. It appears the bug is caused by iOS not handling the Unicode encoding of the foreign characters correctly, causing the iMessage app to crash when displaying the notification of the incoming message.
When received, the iPhone will instantly crash and reboot unless the user is currently in the iMessage app, which will itself crash. Some have reported that they can no longer access their messages at all after the app crashes.
The string of text is very specific and it is unlikely anybody would experience this during normal use. You may want to be wary of friends with a tendency to play pranks though as it is easy to see how you could be ensnared in reboot loops.
The Guardian notes that the bug also occurs in Arabic, Marathi and Chinese languages. It is caused by iOS shortening messages with an ellipsis in the banner notifications. The reboot occurs when the ellipsis is placed in the middle of a string of non-Latin characters.
Once the text has been received, iMessage will continually crash. There is a way to undo the damage though. The suggested method is to use Siri to send yourself a message, clearing the notification. You can also reply to the message in iMessage on a Mac. If anyone else sends you a text, that will also cancel it out.
For now, the exploit doesn’t have any serious associated effects. It is being used as a prank tool by several Twitter users but beyond annoying iPhone users it doesn’t appear to have any more serious security implications.