Microsoft Spoofed Route Pointer Vulnerability Patch is a patch that eliminates Windows vulnerability that could allow source routing to be performed, even if it has ostensibly been disabled. The vulnerability exists in Windows 95, 98 and Windows NT 4.0. The patch also includes added functionality to provide additional control over source routing. Windows NT 4.0 Service Pack 5 introduced the ability to disable source routing on a multi-homed Windows NT machine that acts as a router. However, even if source routing is disabled, it is possible to bypass it by including a specific type of incorrect information within the route pointer in the data packet. Windows 95 and 98 also provide this capability, and are affected by the same vulnerability. The patch restores correct operation to the anti-source routing feature. In addition, it provides additional functionality that enables source routing to be disabled on single-homed machines and on multi-homed machines that are not used as routers. Customers who are using multi-homed Windows 95, 98 or or Windows NT machines, and who wish to disable source routing should apply the patch to ensure proper operation of the anti-source routing features. In addition, customers who have non-routing machines in vulnerable locations (for example, single-homed machines outside of a firewall or multi-homed machines joining two subnets) may wish to install the patch in order to use the new functionality to disable source routing in these cases as well.