Your WhatsApp account might get hacked by opening an Mp4 file. Yes, this is true. Hackers are now using a new whatsapp Mp4 bug attack to get access to a user's account.
The good news is, Facebook has been able to make a patch to protect this attack. But, the fact is, not all users updated their app to the newest version. Those users are seriously in danger of using some older version of WhatsApp.
Facebook has successfully released the patch. But that is not available for all users as they are still working on it.
Keep yourself safe from the hackers by installing the latest whatsapp update. You need to be carefull while opening mp4 files. Avoid if you find any file suspicious.