White screen of death errors
The error you've shown is from someone running a hacking script.

The nginx documentation offers many solutions to avoid running bad php scripts in their Pitfalls and Common Mistakes FAQ, but the one I like is the try_files directive to only run scripts that exist on your server otherwise return a 404 Not Found status code.

location ~* \.php$ {
    try_files $uri =404;
    fastcgi_pass backend;
    # [...]
}