Malware Missed in scan

I was recently contacted by my webhost stating there were malicious codes embedded in my website.
I redid an ithemes malware scan which turned everything up good still, and my site is pretty high on security through the plugin.

They want me to remove the malware and then get back to them so they can rescan my site, so Im figuring they are going to have to lock it if I don’t figure out how to fix it. I really have no clue how to change these files individually or where the code is embedded in it to change it so I’m figuring my only choice is to reinstall.

My issue is why isn’t your plugin seeing this in it’s scan? Everything is current and up to date.

These are the infected files they listed:
public_html/oldindexhtml.zip
/public_html/wp-admin/about_indesit.php
/public_html/wp-admin/load-styles_backup.php
/public_html/wp-admin/user/menu_bck_old.php
/public_html/wp-admin/css/colors/_variables_indesit.php
/public_html/wp-admin/css/colors/ectoplasm/colors-rtl.min_ver1.php
/public_html/wp-admin/css/colors/ectoplasm/colors-rtl.min_indesit.php
/public_html/wp-admin/css/colors/light/colors-rtl.min_prevv1.php
/public_html/wp-admin/css/colors/blue/colors-rtl.min_ver1.php
/public_html/wp-admin/css/colors/midnight/colors.min_backup.php
/public_html/wp-admin/css/colors/midnight/colors_bck_old.php
/public_html/wp-admin/css/colors/sunrise/colors-rtl.min_old.php
/public_html/wp-admin/css/colors/sunrise/colors-rtl.min_backup.php
/public_html/wp-admin/includes/plugin-install_ver1.php
/public_html/wp-admin/includes/class-wp-upgrader-skins_bck_old.php
/public_html/wp-admin/network/site-info_indesit.php
/public_html/wp-admin/network/site-themes_old.php
/public_html/wp-admin/js/inline-edit-tax.min_backup.php
/public_html/wp-admin/js/xfn_indesit.php
/public_html/wp-admin/maint/repair_infoold.php
/public_html/wp-content/themes/its-a-girl/functions.php
/public_html/wp-content/themes/magazino/functions.php
/public_html/wp-content/themes/cleanpress/functions.php
/public_html/wp-content/themes/coller/functions.php
/public_html/wp-content/themes/vryn-restaurant/functions.php
/public_html/wp-content/themes/hanamoto/functions.php
/public_html/wp-content/themes/hanamoto/js/jqueryui/437a1895_backup.php
/public_html/wp-content/themes/preus/rtl_backup.php
/public_html/wp-content/themes/preus/functions.php
/public_html/wp-content/themes/preus/css/nivo/slider/themes/bar/bullets_indesit.php
/public_html/wp-content/themes/preus/inc/js/media-uploader_noversion.php
/public_html/wp-content/themes/sugar-and-spice/functions.php
/public_html/wp-content/themes/frau/functions.php
/public_html/wp-content/themes/the-erudite/functions.php
/public_html/wp-content/themes/gridster-lite/functions.php
/public_html/wp-content/themes/monaco/functions.php
/public_html/wp-content/themes/monaco/js/navigation_prevv1.php
/public_html/wp-content/themes/sketchbook/functions.php
/public_html/wp-content/themes/sketchbook/css/960_16_col_infoold.php
/public_html/wp-content/themes/sketchbook/doc/assets/e73dff55_noversion.php
/public_html/wp-content/themes/sketchbook/admin/options-interface_ver1.php
/public_html/wp-content/themes/market/functions.php
/public_html/wp-content/themes/Felice/functions.php
/public_html/wp-content/themes/dinky/functions.php
/public_html/wp-content/plugins/related-content-by-wordnik/_indesit.php
/public_html/wp-includes/SimplePie/Content/44dd7011_infoold.php
/public_html/wp-includes/SimplePie/HTTP/Parser_old.php
/public_html/wp-includes/SimplePie/XML/Declaration/Parser_backup.php
/public_html/wp-includes/Text/Diff/Renderer_bck_old.php
/public_html/wp-includes/Text/Diff/Renderer/inline_indesit.php
/public_html/wp-includes/js/thickbox/thickbox_backup.php
/public_html/wp-includes/js/mediaelement/controls_indesit.php
/public_html/wp-includes/js/tinymce/license_new.php
/public_html/wp-includes/js/tinymce/utils/form_utils_infoold.php
/public_html/wp-includes/js/tinymce/skins/3aa3d81d_noversion.php
/public_html/wp-includes/js/tinymce/skins/wordpress/images/video_ver1.php
/public_html/wp-includes/js/tinymce/skins/lightgray/fonts/tinymce_indesit.php
/public_html/wp-includes/js/tinymce/plugins/wpautoresize/plugin.min_bck_old.php
/public_html/wp-includes/js/tinymce/plugins/colorpicker/plugin.min_bck_old.php
/public_html/wp-includes/js/tinymce/plugins/compat3x/plugin_old.php
/public_html/wp-includes/js/tinymce/plugins/compat3x/css/dialog_new_prevv1.php
/public_html/wp-includes/js/tinymce/plugins/compat3x/css/dialog_new.php
/public_html/wp-includes/js/tinymce/plugins/wpview/plugin_infoold.php
/public_html/wp-includes/js/tinymce/plugins/hr/plugin_new.php
/public_html/wp-includes/js/swfupload/handlers_infoold.php

https://wordpress.org/plugins/better-wp-security/