$login_query = $db->query("SELECT * FROM " . DB_PREFIX . "admins WHERE
    username='" . $admin_username . "' AND password='" . md5($admin_password) . "' AND level='1' LIMIT 0,1");

$is_login = $db->num_rows($login_query);

$login_output['admin_exists'] = false;
if ($is_login)
{
    $login_output = login_user($username, '', '', true);
    $login_output['admin_exists'] = true;
}