A little theory I came up with:
Ping; A protocol that sends a message to another computer and waits for acknowledgment, often used to check if another computer on a network is reachable. (http://www.answers.com/ping
Often times, we use pinging, as a method to test how good of a connection one computer has to another. This is possible by the host, which originally requested the ping, to meassure the time it took the client to respond.
I believe it is possible to meassure the patterns of how often a ping request is sent to an Xbox 360, and send a false or spoofed, ping reply shortly before the Xbox 360 is expecting the next ping request. As long as the host recieves the reply after it sends the request, it will trick the host into thinking it is a legitimate response.
The purpose is to make the server think you have an excellent connection, possibly making lagswitches more sophisticated, and guarunteeing you a 99% chance (percentage pulled out of my ass) of getting party leader for parties.
Flaws in the theory: if the host sends a string in the message, that the Xbox 360 must match in the response, then there will need to be a system to guess that string. If the string is random, then it might be impossible.