GameSpy has a bit of a monopoly around online services for multiplayer games, including server listings etc. They use a lame XOR encryption technique to ‘restrict’ third party access to these master servers. Fortunately, due to their monopoly they can’t really quickly change things without breaking it all, and thus the algorithm has been documented and became available for opensource developers thanks to the efforts of Luigi Auriemma of http://aluigi.altervista.org.

Unfortunately GameSpy then decided it would be good to threaten him with litigation.

Yay. Go Go GameSpy. Read about this pretty sad story at http://aluigi.altervista.org/papers.htm#distrust