Why is Server 2003 rated as Important?
Server versions of Windows such as Windows Server 2003 are not vulnerable to the IGMP code execution vulnerability. WS03 does not enable UPnP (Universal Plug and Play) by default,
and no other services use multicast.
As a result, the WS03 machine will ignore IGMP messages received from the network.
UPnP is a network service that relies on IP multicast,
and is only enabled by default on Windows XP and Windows Vista.