This patch eliminates a security vulnerability that could cause an affected system to fail, and depending on the number of affected machines on a network, potentially could be used to flood the network with superfluous data. The affected system component is normally present only if it has been deliberately installed.The Microsoft IPX/SPX protocol implementation (NWLink) includes an NMPI (Name Management Protocol on IPX) listener that will reply to any requesting network address. The NMPI listener software does not filter the requesting computer's network address correctly, and will therefore reply to a network broadcast address. Such a reply would in turn cause other IPX NMPI listener programs to also reply. This sequence of broadcast replies could generate a large amount of unnecessary network traffic. A machine that crashed due to this vulnerability could be put back into service by rebooting.IPX is not installed by default in Windows 98, 98 Second Edition, or Windows Me, and is only installed by default in Windows 95 if there is a network card present in the machine at installation time. Even when IPX is installed, a malicious user's ability to exploit this vulnerability would depend on whether they could deliver a malformed NMPI packet to an affected machine. Routers frequently are configured to drop IPX packets, and if such a router lay between the malicious user and an affected machine, they could not attack it. Routers on the Internet, as a rule, do not forward IPX packets, and this would tend to protect intranets from outside attack, as well as protecting machines connected to the Internet via dial-up connections. As discussed in the FAQ, the most likely scenario in which this vulnerability could be exploited would be one in which a malicious user on an intranet would attack affected machines on the same intranet, or one in which a malicious user on the Internet attacked affected machines on their cable modem or DSL subnet. Read the ""Malformed IPX NMPI Packet"" Vulnerability FAQ.