Hello Simon,
Thank you for your feedback on this.
The deactivated files should now return a 404 when being accessed.
You can deactivate any of your files if you are logged in with the account that created them. Go to the file and click the red deactivate link to deactivate. The next time you or anyone tries to visit the file you should get a 404 message. You can get a list of your active files here:
http://my.creativecow.net/Simon-Ubsdell/files
Abraham