Code Vanished

[gasg]

Is the SMF 1.1.RC2 auto correction code?
It is very very strange, I've add some times a go this code
// Redirect users who try to access /forum directly
if (strpos($_SERVER['QUERY_STRING'], 'dlattach') === false)
{
        if(!defined('_VALID_MOS')){ header("Location: /index.php?option=com_smf&Itemid=yourItemidNum");}
}

To the SMF index.php to redirect to wrapped forum in to my joomla portal, today I have opened this file for some reason, but this code had vanished without installing any package or manual modification anywhere in the php's Board files...
what happened?