Dynamic Downloads in PHP

[Reven]

I want to create a script which will allow people to download files, but through dynamic links. For example, instead of using a static link such as example.com/files/file1.zip, where hot-linking can occur, I would like to do something like example.com/files/filedownload.php?file=file1, in which I can do checks to make sure the person downloading is logged in to vBulletin and stuff.

I don't know the name of the process of generating dynamic downloads, so I can't find anything on php.net. All I can think of doing is changing the header to the mime type of the file, but I don't know then how to start the download without the user having to click on something.

I don't want to redirect to the static file location either, as this is a security risk.

Any help would be fab. Cheers.