Microsoft has responded to my report to secure@microsoft.com and I can now disclose what I found. There is a minor bug on the MS Server 2008 DNS service that responds with the list of all root servers when queried for non-authoritative domains, EVEN when recursion is set to OFF. This allows a malicious party to spoof the source ip on a udp DNS request to any MS Server 2008 DNS and elicit a 533 byte response to a victim, making the server a contributor to coordinated Distributed Denial of Service attacks. The response contains the default list of root DNS servers. Version tested: MS DNS on MS Server 2008 R2 version 6.1.7601.17514 Server is Authoritative to only one .com domain. Config Parameters: DNS Recursion set to "disable" Enable Round Robin Enable Netmask Ordering Secure Cache against pollution And My Mitigation steps: Remove all root DNS servers listed on the "Root Hints" tab. This will not negatively affect the DNS functionality of the server when deployed only as an authoritative server for a specific domain. Although RFC1034 on page 21 does allow the DNS to reply with the list of root servers (if configured) as a response option, ultimately it is preferable for it to mimic the behavior of BIND and not respond at all under these test conditions, to discourage abuse from malicious entities. More details with images and packet captures and MS responses, in my web file http://pe.lka.com/ Pedro CCNP, CCDA, CCNA-Security, SANS GPEN ...But mostly a curious guy.