Well, if it's covered by a patent, then it can't be covered by any NDA, since by definition a patent is disclosed. Of course, if it is covered by a patent, there are other problems...
Otherwise, it would depend how broadly written any NDA/non-compete/whatever agreement was that he had signed with Microsoft. Some companies in the past were notorious for overly-broad non-compete agreements, so broad as to render you virtually unemployable if you left the company. However, I've never heard that Microsoft went in for that sort of thing.
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Otherwise, it would depend how broadly written any NDA/non-compete/whatever agreement was that he had signed with Microsoft. Some companies in the past were notorious for overly-broad non-compete agreements, so broad as to render you virtually unemployable if you left the company. However, I've never heard that Microsoft went in for that sort of thing.