You should apply that to the entire UBB.threads directory; or, if you insist on doing it per directory, it'd need to be applied to:
/cache
/cache_builders/custom
/gallery
/images (if you want to allow uploads from the control panel)
/includes
/languages (if you want to be able to use the editor)
/sessions
/styles (if you want to be able to create/manage styles)
/templates/compile
/tmp
/uploads (if you're using this directory for uploads)

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