After a "Defender" scan, I have gotten an email with this message:
"......I've finished scanning your site for vulnerabilities and I found 3 issues that you should take a closer look at!
/wp-includes/images/crystal/license.txt This WordPress core file appears modified
/wp-includes/default-constants.php This WordPress core file appears modified
/wp-includes/default-constants-old.php Unknown file in WordPress core