A bug dubbed the "Black Dot message" is currently doing the rounds on iOS devices and when viewed, causes the iMessage app to crash. Fortunately, it doesn't completely freeze the iPhone or iPad and only affects those devices running iOS 11.3 or the iOS 11.4 beta.
EverythingApplePro discovered the message and has uploaded a video to YouTube detailing what it does. The message itself features a black dot with a hand pointing towards it. Seems pretty harmless, right? Wrong. The message actually contains a whole string of hidden characters that normally tell the messaging how to read messages, whether it be right to left or left to right.
The issue is that there as so many of these characters within the message, that the processor inside the iPhone or iPad can't deal with it, which then causes iMessage to crash. If you force close iMessage and go back into it, it will still be frozen.
The Black Dot bug is reminiscent of the text messages that went around at the beginning of 2017 that caused iOS devices running iOS 10 to crash and the Black Dot message has already been seen in WhatsApp on Android devices, causing a similar reaction. However, that version only caused the app to crash if users tapped on the message.
A couple of workarounds to fix the issue include forcing iMessage to close and then using 3D Touch on the app icon to create a new message, or deleting it from another iOS device or Mac connected to the same Apple ID. If you see the message come through as a notification at the top of your screen, whatever you do, don't open it.
Apple hasn't released a fix for the bug itself just yet, but is expected to very soon.