terminating sessions & cookies

[buducom]

<?
session_start();

setcookie(muid, $passwordis2, time()-3600,"/");
$SESSION["passwordis"] = "";
$SESSION["muid"] = "";

$_SESSION["muidde"] = "";
session_destroy();
header("Location: http://www.backtohome.com");
?>

Why is this not working?
it seems the session keeps on running and running and running no matter how often i try to logout.

[devinemke]

what is "muid"? are you sure you don't mean $muid, or are you using the literal string "muid", if so you must pass it to setcookie() in quotes.