Scanning for unpackaged files

[Martin Fuzzey <mfuzzey@tele2.fr>]

Hi all,

I am looking for a way to find any files on my system in certain 
directories (such as /usr/lib, ...) that have NOT been installed by a 
package.
I know about debsums but that only tells me if packaged files have been 
modified.

I probably could write a script to do it something like this (pseudo code).
   for all installed packages:
       dpkg -L >> all_packaged_files
  
   find > all_files
   sort all_packaged_files
   sort all_files
   diff all_packaged_files all_files

But before I go and do this does anyone know of an existing tool I could 
use?

Thanks,

Martin