URLScan Security Tool:
"UrlScan version 2.5 is a security tool that restricts the types of HTTP requests that Internet Information Services (IIS) will process. By blocking specific HTTP requests, the UrlScan security tool helps prevent potentially harmful requests from reaching the server. UrlScan 2.5 will now install as a clean installation on servers running IIS 4.0 and later.…"

http://www.microsoft.com/technet/security/tools/urlscan.mspx