The makers of the Angry Birds app are being sued by a tiny American company which claims it owns patents on the method used to buy new levels inside the game – a move which has already put off a number of UK developers from selling mobile apps in the US.

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Lodsys, apparently a one-man company based in Marshall, Texas, has named Finland’s Rovio in a patent lawsuit in a Texas court, and has also begun suing some of the biggest names in mobile gaming, including Electronic Arts, Atari, Square Enix and Take-Two Interactive.

The growth of lawsuits in the US by so-called “patent trolls” – which do not make anything but simply demand payments after assertingintellectual property rights – threatens to snuff out the booming mobile app market, which is expected to be worth £4.5bn this year and double that in 2012. A number of patent-owning companies have begun lawsuits in the US against more than a dozen software companies. However, many small independent developers find the costs of a lawsuit too onerous, even given that they could run into thousands of dollars.

The US patent system allows software implementations of ideas to be patented, which differs significantly from the European Union – although the European Parliament has been considering aligning patent rights with the US.

Lodsys owns patents granted between 1999 and 2009, and first filed claims against seven defendants last May. It has now removed one of those, Wulven Games, but added Rovio’s versions of Angry Birds for iPhone and Android, as well as EA’s The Sims 3 for iPhone, Atari’s Greatest Hits compilation for iPhone and iPad, Square Enix’s Big Hit Baseball for iPhone and iPad, and Take-Two Interactive’s 2K Sports NHL 2K11 for iPhone.

Florian Mueller, a specialist in intellectual property lawsuits, says that the move shows the company is “not afraid of suing deep-pocketed app developers”: it is already suing the computer giant HP, as well as clothing company Adidas, retailer Best Buy and the New York Times. Mueller also points out that bringing Angry Birds into the case makes it clear that Lodsys is going after developers writing apps for phones using Google’s Android software, which now make up the best-selling smartphones, as well as those writing for the iPhone and iPad.

Lodsys is asking for injunctions and damages in its complaint, although the company has not yet published an update on its blog to explain its decision to add the five new games companies to the lawsuit.

The news is likely to increase Apple’s involvement in the case on behalf of its developers. In June, the company filed a motion to intervene in the case, claiming that its existing licence for the patents in question also covers iOS developers – which Lodsys disputes.

“While the developers will likely be interested in resolving this case as quickly and inexpensively as possible, Apple’s interest is in protecting its broader license rights with respect to thousands of App developers for Apple products who may be the subject of future Lodsys lawsuits or threats,” said Apple’s motion, making it clear that the company did not expect the small independent developers originally sued by Lodsys to be able to fight the company in court.

Last week several European independent developers said they were withdrawing their apps from the US App Store for fear of being sued by Lodsys. That is clearly not an option for the likes of Rovio and EA, as well as for Apple. Games are the most lucrative category on the App Store, with iOS remaining the lead mobile platform for the vast majority of mobile games firms.

At the time Lodsys sent its original letters to developers demanding they settle or be sued, Mueller wrote that “It’s actually questionable whether Lodsys’s patents would survive a well-funded effort to have them declared invalid.”

[Gaurdian]