Template problems

You’re website is being hacked. Secure the site/hosting.

This may help: https://codex.www.ads-software.com/FAQ_My_site_was_hacked

I know the site has been hacked, or at least they try to hack it. I don’t know how to avoid it or what to do to solve it. Anyone an idea?

Eh.. did you read the page I linked to before ?
Also: https://codex.www.ads-software.com/Hardening_WordPress

Yes, I read it. There was never a problem with this site till the last theme was replaced by Oria. The rule that is added has something to do with the theme Oria. Because I have the latest version of wordpress and the latest version of the theme Oria I asked if there was someone who recognised this problem. Maybe it is known by the developers of Oria?

Hello, please try installing the WordFence security plugin and doing a scan of your website so it could find any malicious code and prompt to remove them, you might also need to hire a freelancer to help get rid of the security issues and secure your site.