Scan results show modified theme or plugin files
If you have customized the default WordPress themes such as TwentyFifteen, without creating a “child theme“, you will see the files listed as changed if you have enabled “Theme Scanning” in Wordfence. You can safely ignore these warnings if you are sure that it was you who changed those files.
If you have downloaded an open-source theme or plugin from the WordPress repository and have modified it, you will also get warnings about the modified files. You can also choose to ignore these warnings in the scan results if you are sure that it was you who modified the files.
For each modified file, you can click "See how the file has changed" to view a comparison of your file with the official file.
More details about scan results can be found on the Wordfence scanning page.