Protect uploaded files/images

Hi there,

I am looking for a way to make uploaded files visible to logged in users only. It is easy to protect posts but if you know the path to where the uploads are you can download them.
There are two plugings (private files & secure files) which claim to do what I want. Especially private files sounds good because it uses htaccess which seems to be pretty safe bute the plugin is not working.
So if you know how to protect uploaded files but make them available to logged in users please let me know.
Thanks!