Ok, backup made.
Log from Wordfence below:
[Mar 06 22:16:45]Preparing a new scan.Done.
[Mar 06 22:16:45]Remote scan of public facing site only available to paid membersPaid Members Only
[Mar 06 22:16:48]Fetching core, theme and plugin file signatures from WordfenceSuccess.
[Mar 06 22:16:50]Fetching list of known malware files from WordfenceSuccess.
[Mar 06 22:16:52]Comparing core WordPress files against originals in repositoryProblems found.
[Mar 06 22:16:52]Skipping theme scanDisabled [Visit Options to Enable]
[Mar 06 22:16:52]Skipping plugin scanDisabled [Visit Options to Enable]
[Mar 06 22:16:52]Scanning for known malware filesSecure.
[Mar 06 22:16:54]Scanning file contents for infections and vulnerabilitiesProblems found.
[Mar 06 22:16:54]Scanning files for URLs in Google's Safe Browsing ListSecure.
[Mar 06 22:17:18]Scanning posts for URL's in Google's Safe Browsing ListSecure.
[Mar 06 22:17:19]Scanning comments for URL's in Google's Safe Browsing ListSecure.
[Mar 06 22:17:19]Scanning for weak passwordsSecure.
[Mar 06 22:17:20]Scanning DNS for unauthorized changesSecure.
[Mar 06 22:17:20]Scanning to check available disk spaceSecure.
[Mar 06 22:17:20]Scanning for old themes, plugins and core filesSecure.
[Mar 06 22:17:20]Scan complete. You have 843 new issues to fix. See below for details.
There is a lot of "This file may contain malicious executable code" with "View this file" and "Delete this file" option.
There isn't Repair option
And a lot of "WordPress core file modified:..... " with "View...", "Restore to original..." and "Show how the file was changed"
What next I can do?