Microsoft used their own implementation of Kerberos. From the Kerberos Wikipedia entry:

> While Microsoft uses the Kerberos protocol, it does not use the MIT software.

The license of the original implementation is thus irrelevant. Pretty much the only thing that would have prevented MS would have been if there were patents on Kerberos.

Did MS use kerberos implementation or the protocol, wiki page isn't very clear on it. If it is 2nd then it would be an entirely different issue, which even GPL/copyleft wouldn't have helped (though oracle java lawsuit may do so).

Yes, they used the code itself (which was legal due to the 3-clause license), but didn't credit until publicly shamed. There was a huge stink back in the day because of it.

MS extended the protocol, not the implementation.

How would the Oracle lawsuit change anything? Protocols are almost explicitly the things that are not protected by copyright. The problem is, people here are confusing interfaces in human-readable code (copyright-eligible) with interfaces for binary interoperability between systems (not eligible).

no dude, not only did they take the code and extend the protocol[1], while attempting to relicense it[2], but then they tried to sue /. to remove posts of people that talked about it[3].

1. http://www.heise.de/newsticker/meldung/Microsoft-und-Open-So... 2. http://slashdot.org/story/00/05/02/158204/kerberos-pacs-and-... 3. http://features.slashdot.org/story/00/05/18/2015251/our-atto...