The author, Computer User, comes clean about it here.
The interesting thing is that the code as posted by CU originally would have worked, it did indeed brute force keys and pound them against Vista. The problem? It would have taken an awful long time to get a result, too long to be practical.
That said, there are probably a bunch of malware trojans masquerading as the keygen now, so it is probably best avoided. µ
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