This update to internet Protocol Security Clients IPSec & L2TP/IPSec allows IPSec to work across Network Address Translation (NAT) boundaries. A client may connect to a Windows Server 2003 Server with IPSec or L2TP/IPSec when the client is behind one or more NATs. Users should download this update if they use IPSec &/or L2TP Virtual Private Network (VPN) connections. After you install this item, you may have to restart your computer. Once you have installed this item, it cannot be removed.