Hacked By Moroccan Revolution Team

This website has been hacked by ISIS supporters. Not sure what caused the vulnerability as Wordfence was running with daily scans both in and outside of the wordpress folder.

Website opens with a black screen a message that says “Hacked By Moroccan Revolution Team” and the ISIS logo with contact details and propaganda music playing.

Does any one have any idea whether it would be possible to identify the code causing this screen?
The link to the website is https://www.bona-fide.co.za

Any help would be appreciated as I hope this will also help all WordPress users by perhaps identifying the problem.