Microsoft Legally Contradicts Itself

In what seems to be a new and much welcomed trend towards true openness, Microsoft announced yesterday they were opening up the source code of .NET under a Free Software License. And they weren’t kidding: the code for .NET can already be found at their GitHub repository.

The repository contains the foundational libraries that make up the .NET core development stack. It also contains a MIT license, a valid, albeit non-copyleft, free license (i.e., third parties can still build proprietary software from the code), and a file named PATENTS.TXT.


The PATENTS.TXT file contains Microsoft’s legally binding promise not to sue anybody for patent infringement if they use the code. Sort of. The problem is that the wording of the document opens a potential loophole that would allow Microsoft to sue a third party that took parts of the .NET code and built or included it into another application for patent infringement.

From the PATENTS.TXT file:

“Microsoft Corporation and its affiliates (“Microsoft”) promise not to assert any .NET Patents against you for making, using, selling, offering for sale, importing, or distributing Covered Code, as part of either a .NET Runtime or as part of any application designed to run on a .NET Runtime.”

You are explicitly allowed to sell, distribute and import, and create code for the runtime, but there is no mention of modifying the runtime code itself or taking bits of the code and incorporating it into your own code. And if its not mentioned, does that mean it can be subject to litigation despite the MIT license?

We do not know at this stage whether this is an oversight, or that old habits die hard and they are finding difficult to let go completely, or whether Microsoft is really trying to poison the FLOSS well. Whatever the agenda, hidden or not, this should be addressed as soon as possible. Microsoft should amend the promise to close the loophole and avoid the contradiction that it creates with the MIT license that does explicitly allow modifying and moving parts of the code to other products.

Thanks must go to r/linux for pointing this out. Nothing gets past you guys.

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