I SOLVED IT. I found a hidden module, not installed by me, called SENDINBLUE. This module is not visible on the site, but only with FTP. I solved it like this: 1. Deleted the SENDINBLUE folder, 2. Deleted Scan.php from the root of the site, 3. Deleted the first strings from the index.php file, because they were not present in the index.php of the backup 4. Delete file virus created in lang folder (index.php, sitemap.xml and robots.txt) and Restored the language files located in the theme's lang folder (index.php, it.php, en.php).
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I SOLVED IT. I found a hidden module, not installed by me, called SENDINBLUE. This module is not visible on the site, but only with FTP. I solved it like this: 1. Deleted the SENDINBLUE folder, 2. Deleted Scan.php from the root of the site, 3. Deleted the first strings from the index.php file, because they were not present in the index.php of the backup 4. Restored the language files located in the theme's lang folder (index.php, it.php, en.php).