Restore old version or Upgrade ?

I think a simple upgrade to 2.8.5 would be easier than figuring out which files to replace in the old install. Don’t overwrite wp-content and so you”ll keep your theme. You might also need How to Completely Clean a Hacked WordPress Install.

if you dont know what version you started with “a simple upgrade” may not be that simple.

whats inside wp-includes/version.php ?

My bad; they should know which version they run now before replacing/upgrading….

Looks like it’s running 2.8.4, which would be close enough to do a quick file delete / replace and database update ?

Yes.