Apple filed a legal brief on Monday insisting it has every right to intervene in Lodsys' attempts to sue iOS developers for using in-app purchasing. The filing is a formal response to the patent firm's claims that Apple has no legal standing to intervene Lodsys' patent infringement suit against various independent iOS developers. Apple originally filed to intervene in the lawsuit after its chief legal counsel unsuccessfully tried to explain that its license for the patents in question covers developers using in-app purchasing APIs in iOS.

Lodsys began threatening both iOS and Android developers with lawsuits in May if the developers didn't pay licensing fees for its claimed in-app-purchasing-related patents. Many independent developers lack the financial and legal resources to litigate a patent infringement claim, so a number of iOS developers began a campaign to get Apple to help, threatening a boycott of in-app purchasing if only to avoid such legal threats.

Lodsys acquired its four patents from former Microsoft CTO Nathan Myhrvold's Intellectual Ventures patent holding company. It turns out that Apple already has a license to those patents by virtue of an investment deal in Intellectual Ventures. That deal gave Apple (among other companies, including Google) a license to some 30,000 or so patents under Intellectual Ventures' control.

Apple Senior Vice President and General Counsel Bruce Sewell noted that fact in a letter to Lodsys, asking the company to "immediately... cease its false assertions that the App Makers’ use of licensed Apple products and services in any way constitute infringement of any Lodsys patent." This defense is known as "exhaustion"—the third parties in question should be covered by the original license, so patent owners can't claim infringement by those third parties.

Lodsys insisted otherwise and shortly filed suit against seven small independent developers. Apple filed a motion to intervene in the lawsuit a week later, citing its need to protect its license to the patents in question and noting that the independent developers targeted by Lodsys didn't have the adequate resources to support Apple's interest in the suit. Lodsys of course claimed that Apple had no reason to intervene, especially after Lodsys added several large game developers, including EA, Rovio, and Atari, to the defendant list.

Apple's most recent brief, though heavily redacted, is adamant that its license to the patents gives it every right to intervene in the case. The company asserts that developers are its business partners, and therefore Apple has a material interest in protecting those partners from being sued over technology that it has previously licensed. The heart of the dispute hinges on the licensing terms Apple received from Intellectual Ventures, though the details of those terms apparently cannot be publicly revealed. Furthermore, according to the brief, "none of the [current] defendants have the technical information, expertise, and knowledge regarding how Apple's technology works or the negotiation and intent of the License itself to fully articulate and develop Apple's exhaustion defense."

Apple has consistently stuck with its exhaustion defense throughout the dispute, despite the fact that Lodsys' patents are widely believed to be invalid. Several companies whose clients were targeted by Lodsys have filed preemptive lawsuits requesting declaratory judgements that Lodsys' patents are invalid, and some independent developers led by former Apple engineer Mike Lee have formed a legal defense fund to fight Lodsys and other patent trolls. Even if Apple believes the patents wouldn't stand up to reexamination, it is suspected that the secret terms of the license agreement with Intellectual Ventures prohibits Apple from attempting to have the patents invalidated.