<?php
// block any attempt to the filesystem
if (isset($_GET['file']) && basename($_GET['file']) == $_GET['file']) {
    $filename = $_GET['file'];
} else {
    $filename = NULL;
}
// define error message
$err = 'Sorry, the file you are requesting is unavailable.';
?>

<?php

if (!$filename) {
// if variable $filename is NULL or false display the message
    echo $err;
} else {
// define the path to your download folder plus assign the file name
    $path = 'downloads/' . $filename;
// check that file exists and is readable
    if (file_exists($path) && is_readable($path)) {
// get the file size and send the http headers
        $size = filesize($path);
        header('Content-Type: application/octet-stream');
        header('Content-Length: ' . $size);
        header('Content-Disposition: attachment; filename=' . $filename);
        header('Content-Transfer-Encoding: binary');
// open the file in binary read-only mode
// display the error messages if the file can´t be opened
        $file = @ fopen($path, 'rb');
        if ($file) {
// stream the file and exit the script when complete
            fpassthru($file);
            exit;
        } else {
            echo $err;
        }
    } else {
        echo $err;
    }
}
?>