Where did the error on the site from superindexator.ru/ come from?

Question

CMS

On the site, after the tag, the following error came out:

<p><a href="http://superindexator.ru/">superindexator.ru</a></p>
    <h1>404</h1>
    <h2>Page Not Found</h2>
    <div>
        It seems that the page you were trying to reach does not exist anymore, or maybe it has just moved.
        You can start again from the <a href="http://superindexator.ru/">home</a> or go back to <a href="javascript:%20history.go(-1)">previous page</a>.
    </div>

Where could she come from?