HackeD by Newo Turkish Hacker

Hi there.
I am using the last version of my instalation, all plugins and themes. Some of my sites got hacked by a Newo.
See the sites https://flow-ideas.com/ https://www.kravodaritel.com/ and https://evropro.org/. It is terrible and annoyng. The admin page is OK, but my email adress is not in the database.
Please tell me how to solve the problem and how to prevent from hacking the other of my sites.
I made a search in google and I found that the same hacker is hacking mostly wordpress sites.