Defending Against Patents

The MPL grants a limited license to the Initial Developer 's and Contributors' patents. But what is the MPL's response if a third party asserts its patents against an Initial Developer or Contributor ?

The MPL handles this in various ways. First, the Initial Developer or any Contributor who learns about such a third party patent claim has an obligation to inform all subsequent licensees :

If Contributor has knowledge that a license under a third party's intellectual property rights is required to exercise the rights granted by such Contributor under Sections 2.1 or 2.2, Contributor must include a text file with the Source Code distribution titled "LEGAL" which describes the claim and the party making the claim in sufficient detail that a recipient will know whom to contact. If Contributor obtains such knowledge after the Modification is made available as described in Section 3.2, Contributor shall promptly modify the LEGAL file in all copies Contributor makes available thereafter and shall take other steps (such as notifying appropriate mailing lists or newsgroups) reasonably calculated to inform those who received the Covered Code that new knowledge has been obtained. ( MPL section 3.4[a].)

A far more dramatic response is authorized by the MPL if someone actually files a patent infringement lawsuit against the Initial Developer or a Contributor (both of whom are now called a Participant and whose code is now called a Contributor Version ). The provision is generally referred to as a patent defense ; it can be found among the MPL's termination provisions in section 8.

The MPL's patent defense provision can be summarized this way: Participant will license you his or her Contributor Version ”with the right to make free copies, prepare derivative works, and distribute ”as long as you don't sue for patent infringement. But if you sue the Participant claiming that the Contributor Version itself infringes your patent, all copyright and patent licenses to you under the MPL for the Contributor Version are terminated. And, if you sue the Participant for any other patent infringement unrelated to the Contributor Version, all patent licenses to you under the MPL for any software are terminated .

The success of a patent defense depends on the perceived value of the Contributor Version to the third party patent owner. For important and valuable open source software, it may be more painful to the patent owner to forgo use of the software than to forgo some potential patent royalties. It at least forces a potential patent litigant to think carefully before he or she sues a Participant for infringement. Patent litigation is no longer risk-free.

Here's how the patent defense provision actually reads in the MPL:

If You initiate litigation by asserting a patent infringement claim ... against Participant ... alleging that:

(a) such Participant's Contributor Version directly or indirectly infringes any patent, then any and all rights granted ... under Sections 2.1 and/or 2.2 of this License shall ... terminate prospectively....

(b) any software, hardware, or device, other than such Participant's Contributor Version, directly or indirectly infringes any patent, then any rights granted to You by such Participant under Sections 2.1(b) and 2.2(b) are revoked .... ( MPL section 8.2.)

This is the first patent defense provision we have encountered in an open source license, and it has proven to be quite controversial and yet widely copied . There are several interesting variations on patent defense in other open source licenses; I will discuss some of these variations later.