this happened to me also today. i was able to figure out that the hacker updated all of my pages and added some malware scripts to every page.
If you are able to access your admin panel then go to your pages section and at the end of every page there will be scripts that are causing problem. remove them and update the pages.
Your website will be working fine
It happened to me. I cleaned up but it came again one day later, even websites with last version of WP, with Wordfence, Block Bad Queries, etc.
Does somene knows where it comes from ? Is it an injection ?