Steve Jobs points to the audience as he announces the software development kit for iPhone app programmers in a March 2008 event. Photo: Jim Merithew/Wired.com

Apple’s legal team has fired back at a patent-owning firm that was threatening to sue iPhone app programmers over usage of in-app payment technology.

Apple stated in no uncertain terms that it planned to protect Apple developers.

“Apple is undisputedly licensed to these patent and the Apple App Makers are protected by that license,” wrote Bruce Sewell, Apple’s general counsel, in a response to Lodsys (.pdf) sent Monday. “Apple intends to share this letter and the information set out herein with its App Makers and is fully prepared to defend Apple’s license rights.”

The patent firm Lodsys on May 13 sent letters to several iOS app programmers, claiming that it owned a patent related to the usage of an “upgrade” button, allowing customers to upgrade from a free version of an app to a paid version, or to make purchases within apps. The letter demanded that programmers pay a licensing fee for the patent, or face legal action from Lodsys.

In the technology industry, large companies are already tangled in legal disputes over patents on technologies they claim to have invented or pioneered. For instance, Nokia filed suit against Apple in 2009 for patent infringement, Apple filed a patent lawsuit against HTC in 2010, and Microsoft has gone after Google’s partners offering Android-powered products.

However, with the case of Lodsys, it was odd to see a patent firm shaking down smaller companies for using technologies provided by a larger company.

Apple’s letter said that the technology that Lodsys claims it patented — a user interface that enables interactions with a user to elicit user feedback — requires the use of APIs provided by Apple to the app programmer. Therefore, because Apple owns a license for Lodsys’ patents, they extend to programmers that use Apple’s technologies, too.

Dave Castelnuovo, creator of the popular iPhone game Pocket God, was one of the first programmers to receive Lodsys’ letter. His lawyer David Alberti told Wired.com that Lodsys’ claims made against app developers seemed like a “very far stretch,” because the patents in question seemed to relate to feedback systems on hardware, such as a fax machine, and not technology in a pure software environment.

Lodsys owner Mark Small, who sent the initial letter to app developers, did not immediately respond to a request for comment.

Pocket God maker Castelnuovo said he was happy to see Apple respond very quickly and publicly to Lodsys.

“It shows that Apple cares about its developers and they are willing to stick up for them when something like this occurs,” Castelnuovo told Wired.com.

James Thomson, app programmer of the pCalc scientific calculator app for iPhone, was one of the first to receive Lodsys’ letter. He told Wired.com he was glad Apple was getting involved, but the fight is not over yet.

“I’m just relieved to hear that Apple’s got our backs,” said James Thomson, one of the first to receive the legal threat from Lodsys. “Of course it’s not over until Lodsys withdraws their claims, but this is a big step. I will sleep a lot better tonight, that’s for certain!”

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