This article will explain why you see the message, Your core files have been modified.

What are Core Files?

Core files are created by the WordPress developers and are required for WordPress to run. This does not include Themes or Plugins which may be added on to your site.

Why You See This Message

The message will appear when the core files for your WordPress site differ in any way from the core files that come with WordPress normally. Even slight changes like an extra blank line will cause this error. It doesn't matter if the functionality of the file changes. The core files in WordPress can be modified for many reasons.

You may see this message because:

• You or a developer have customized the core files of WordPress so that they differ from the default core files.
• A plugin or theme has changed the core files of WordPress.
• Malware has infected your site and changed the core files.

If you haven't installed any plugins or themes recently, and haven't modified the core files yourself its possible the site may be infected with malware. Keep in mind seeing this message is not proof of Malware in your site.

If You Think Your Site Is Infected

When you see this message, you will be given the option to click the update button. If you click the update button it will replace the core files with the latest version of the files from WordPress. This will undo any changes made by malware the core files. Don't do this if you have made your own customizations to the file as this will undo those changes as well.