Microsoft provided us with this response to the Teredo report:

It is our understanding that the Symantec report is not final yet, and we are providing the company with our feedback. To be clear, Teredo is primarily designed for consumers to provide global IPv6 connectivity over the Internet and enable peer to peer applications, such as Windows Meeting Space over Internet, Skype, Bit-torrent, etc., that might be blocked by the NAT function of home routers. Teredo provides a way for these applications to communicate over the internet without having to do special router configuration. Teredo gets disabled automatically for enterprises when a domain environment is detected. For enterprises, there are more business-focused IPv6 transition technologies available from Microsoft and other network vendors, including 6to4 and ISATAP that enable enterprises to deploy IPv6 over current IPv4 networks. More information on these technologies can be found at http://www.microsoft.com/technet/network/ipv6/ipv6coexist.mspx .