With all of the hubbub regarding recent realizations about whether Microsoft is a Linux distributor bound by the GPLv2, and the lack of an expiration date on the coupons exposing Microsoft to potentially be bound by the GPLv3, we should also consider the possible defenses already provided under the current version of the license under which MS is currently distributing SUSE.

Some time back, right around when the latest GPLv3 draft was coming out, Groklaw had a posting regarding the implied patent defenses in GPLv2.

Essentially, the GPLv2 requires you to pass on the rights to use, modify and redistribute the software you receive without imposing further restrictions. It can be argued that Microsoft would also need to grant any necessary rights to its "IP" in order to make this so.

The article discusses four doctrines of implied license, legal estoppel, equitable estoppel, conduct and acquiescence. Regarding the first, legal estoppel, which just means you can't grant a legal right and then snatch it away, the article says:

In the hypothetical case above, the accused infringer has an argument that the elements of legal estoppel are met. Through the GPL, the patentee has granted the accused infringer the right to make and distribute the invention. While usage rights may not be explicitly granted under the GPL, it can be argued they are necessary to effectively practice the rights that have been granted. Both the right to practice the invention (through the GPL) and an attempt to derogate that right (by claiming the licensee has no right to use the licensed invention) are present.

Satisfying the legal estoppel theory also requires showing that the licensor received valuable consideration for the license. One possible item of consideration received under the GPL is the reciprocity agreement -- the promise by the licensee to license any further distribution of the program and any works based on it under the terms of the GPL. In Wang, the proliferation of the plaintiff's technology and adoption of it as an industry standard were enough to form consideration under legal estoppel. The licensee may be able to argue that the benefits any licensor receives from agreeing to comploy with the licensee form sufficient valuable consideration to imply a license by legal estoppel.

Let's imagine, for a moment, that Novell, instead of being a GPL bumbler, turned out to be a Ninja. Then the fact that Microsoft was persuaded to distribute vouchers for SUSE, which is distributed under the GPL, might be a way to tie their hands. It could be argued, as I understand the article to be indicating, that you could argue that Microsoft can't help distribute SUSE and then sue over folks using it. N'est-ce pas? And that would be entirely separate from any patent peace nonsense. And Novell helping Microsoft make Open XML a standard might, in Ninja land, be a way to force it to lose its patent rights.

This sorta reminds me of the argument that SCO couldn't distribute under the GPL and then claim infringement, I can't believe Microsoft fell for it again (assuming they thought up the SCO debacle, as it has seemed). I suppose MS could argue they never accepted the terms of the GPL, but that means they willfully committed 40,000+ instances of copyright infringement against each of the hundreds (thousands, likely) of the authors of the code in SUSE.