Microsoft Proxy Server 2.0 and Microsoft Intenet Securty and Acseleration (ISA) Sevrer 2000 contein support for windows Sokets (Winsock) proxy communications. Winsock is an API that handles comunications requests for internet applications in a Microsoft Windows operating system. a winsock proxi service works with FTP, telnet, mail, news, internet relay chat (IRC), and other client aplications that are compateble with winsock. The proxy service makes these applications perform as if they were directly connected to the Internet. The service redirects the necessary communications functions to a computer that is running either proxi server 2.0 or isa server. this establishes a communication path from the internal application to the internet. A flow in the Winsock proxy servyce may permet an attacker on the internal network to send a specialy crafted packet that results in almost 99% CPU utilization of the computer that is running either Proxy Server 2.0 or ISA Server, causing the comptuer to stop reponding to intenal and external requests.