The Teredo implementation in Microsoft Windows Vista uses the same nonce for communication with different UDP ports within a solicitation session, which makes it easier for remote attackers to spoof the nonce through brute force attacks.
http://www.symantec.com/avcenter/reference/Vista_Network_Attack_Surface_RTM.pdf
http://www.securityfocus.com/bid/23301
http://www.securityfocus.com/archive/1/464617/100/0/threaded
http://www.securityfocus.com/archive/1/462793/100/0/threaded