** DISPUTED ** The default configuration of Microsoft Windows 7 immediately prefers a new IPv6 and DHCPv6 service over a currently used IPv4 and DHCPv4 service upon receipt of an IPv6 Router Advertisement (RA), and does not provide an option to ignore an unexpected RA, which allows remote attackers to conduct man-in-the-middle attacks on communication with external IPv4 servers via vectors involving RAs, a DHCPv6 server, and NAT-PT on the local network, aka a "SLAAC Attack." NOTE: it can be argued that preferring IPv6 complies with RFC 3484, and that attempting to determine the legitimacy of an RA is currently outside the scope of recommended behavior of host operating systems.