Secure documents

Hey i was wondering whether there is a way of making it so that only certain users can see documents uploaded to a certain content type through a cck files.

Currently i have a view that is displaying uploaded PDF's, this view is only accessible by certain users. The problem comes in with the fact that the url to the PDF's arent secure e.g absolutely anyone can get to the url. So basically my view is limited to certain users but if someone was to copy the url to one of the pdf's and send it to anyone else they would be able to view the pdf. This pokes a whole range of security holes in my site =/

If anyone has a solution to this i would greatly appreciated help.