So I have virtual folders active for the forums.

E.g. a link like this works: -http://www.domain.com/folder1/thread-t12345.html
But also this works although it's the same thread: -http://www.domain.com/folder2/thread-t12345.html

This results in duplicates and are even indexed by search engines.
Can I prevent this? Can I force it to only accept the correct "folder"?
Or maybe when the script looks for the thread-ID it redirects to the correct virtual folder automatically.