Disable direct link on attachements?

[EarthDog]

I am heavily relying on private forums (the option allow to read other users posts DISABLED).

This works ok when viewing attachments via attachment.php? .....

But i need to disable anyone that has the direct link to /uploads URl.

How can i do it? I fi use htaccess is it going to be ok when viewing the attachment in the post? Actually there is the only place where i need them to be able to see the attachment..