I have a site in modx, and it's been hacked twice by adding this file /modx/assets/images/files.php which contains
Linux+cfcd208495d565ef66e7dff9f98764da+01+[[]]
I've removed it and after it site removed from DBl(domain block list) but I want to know how can I solve this problem so it won't be repeated again?
You need to remove all malicious files, update your modx, update all plugins/extensions and change all passwords on site/db/ftp.