Now: do you have a recent BACKUP of your site ?
Can you see the security of the folders (should be 755) and of files (should be 644) ?
i don't have a recent backup of my site.
Some folders are with 750 and others with 755. All files except 'config.php'(666) in public_html folder is 644.
So the folders/files are ok.
Doesn't your hosting company provide a backup ?
What kind of plan is that ? Shared ? Managed or Unmanaged ? VPS ?
Is anything ELSE hosted in your plan (other site, other cms) ?
Have you MODIFIED the core or anything else ?