Although Sony has yet to issue a full statement on the matter, it looks as though the malicious message bug has since been fixed - according to a tweet sent from the support account for the PlayStation 4.
Over the weekend, players were warned about a malicious message that was circulating that could effectively brick the PS4 if opened. In order to stop the message from being received, players were advised to switch their messages to private and not accept any from people they didn't know.
We've since fixed the issue, and it wasn't bricking consoles, just sending them into a crash loop that can be quickly fixed in under 5 minutes. Delete the message on the PS mobile app, go into Safe Mode, use Option 5, console back to normal. ^DB
— Ask PlayStation UK (@AskPS_UK) October 15, 2018
Per a tweet sent by the official Twitter support account for the PS4, Sony say that they have "since fixed the issue, and it wasn't bricking consoles, just sending them into a crash loop that can be quickly fixed in under 5 minutes." As to the fix Sony recommended, it's about the same as what was initially suggested when the bug was first noticed.
Simply delete the message via the mobile app, put the console into Safe Mode and select 'Rebuild Database' and voila - console fixed.