Passthru didn't work for me for files greater than about 5Mb. Just adding "ob_end_clean()", all works fine now, including > 50Mb files.
$ToProtectedFile=$pathUnder.$filename
$handle = @fopen($ToProtectedFile, "rb");
@header("Cache-Control: no-cache, must-revalidate");
@header("Pragma: no-cache"); //keeps ie happy
@header("Content-Disposition: attachment; filename= ".$NomFichier);
@header("Content-type: application/octet-stream");
@header("Content-Length: ".$SizeOfFile);
@header('Content-Transfer-Encoding: binary');
ob_end_clean();//required here or large files will not work
@fpassthru($handle);//works fine now
