This was discovered by Researcher Indrajeet Bhuyan who suggests that this bug could actually be used to hide evidence. According to him, “Suppose an attacker have send an abusive message or is blackmailing a victim. Now the victim cannot show the message as proof as once the victim receive the smiley […] the whole chat with the attacker would crash and the victim won’t be able to open it. “The victim will have to delete the entire chat with the attacker in order to use WhatsApp normally.”
However it should be noted that for some reason, this bug seems to only affect the Android version of WhatsApp. It has been pointed out that it does cause some “problems” for iOS users, but not in such a severe way of the app completely crashing like it does for Android users. Right now WhatsApp has a character limit of 6,000, meaning that this 5,000 emoji message can get past it.
Perhaps it has something to do with the way WhatsApp for Android handles memory, or maybe it could just be the way Android handles its own memory which could cause the app to crash, but either way it does seem like a bug that needs fixing. Interestingly enough last year there were similar bugs discovered where a particular message sent to iOS Messages users could cause it to crash, and another similar bug was discovered affecting Skype users as well.