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Anyway, if connecting to MSN requires a client licence key of some sort, I doubt they'd give one to an open-source piece of software, as anyone could then modify the software to violate Microsoft's security in whatever way they hypothetically changed the protocol to stop. So if MS give Gaim a license, it will be for signed binaries of some sort.
Of course, it may be reverse-engineered just like the DVD encryption keys were. Though using that would be strictly illegal.
the rumours may be exaggerated: see http://www.trillian.cc/forums/showthread.php?s=e3454b3177f3c4f4aece1c4fc835273a&threadid=42884