Earlier in iOS there was already a Messages bug that could lead to the crash of the entire system. Now, in iOS 11.3 and 11.4 beta versions, a similar bug has been found called 'black dot'. The system freezes if you send an emoji in the form of a black dot and several symbols in a certain order: <>.
It is not clear what is the reason for this bug, but they say that it appeared in version WhatsApp for Android. There is no solution yet, and users just need to be careful. Force closing Messages and reopening the app with 3D Touch may help. Apple is already working on a solution to the problem, but so far it is completely impossible to protect against the bug.
The problem arises because there are several hidden Unicode characters in the message. The system tries to process them, but nothing happens, and it just hangs. Unicode is a complex set of characters, and some of their combinations can be very difficult for the systems Apple and Google to handle. In this regard, similar bugs appear. This bug may affect Mac computers as well, but this information has not been verified yet.
If you have one of the aforementioned versions iOS installed, wait for an update with a bug fix.
Unicode is an integral part of the messaging system, so it is simply impossible to defend against all potential bugs. Nevertheless, the more such bugs are found, the more secure the next versions of systems become. It may take some time to fix the bug, but users can be sure that it will appear in the next update.