Sécuriser une page index

Bonjour,

C'est la deuxième fois qu'un site dont je m'occupe est "piraté".
En tapant l'url du site, un encart rouge apparaît indiquant que le site est malveillant.

J'ai trouvé sur la page index, un script qui n'avait rien à faire là!
je l'ai supprimé, pensant que tout était rentré dans l'ordre.

Rebelote...
Cette fois ci, du code avec un code (en display none bien entendu...) intégrant des liens hypertextes:
Le voici plus bas.
Comment puis-je sécuriser ce site pour que ça ne se reproduise plus?
Merci!

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