Angry Birds developer Rovio is the latest app developer to be dragged into the Lodsys patent lawsuit, which also makes claims against, among others, gaming giants Electronic Arts, Atari, Square Enix and Take Two. The company filed a suit against seven developers back in May, but has now amended it to include the biggest names in the app world.

The total number of defendants in the suit now totals 11, with one company being omitted (Vietnamese company Wulven Games) in the amendment.

The new complaint claims that each of the company's listed has infringed several of Lodsys' patents related to in-app purchases. And with Angry Birds now included, it has targeted an Android app for the first time - Rovio is accused of infringement on both iOS and Android, the rest on Apple's iOS alone.

Lodsys is a US patent licensing company that acquired the patents of inventions created by Harvard Graduate Dan Abelow back in 2004, and known official licensees include Microsoft, Nokia, Google and Apple. And it is with the latter that there is some confusion.

Some developers believe that, as they have used Apple's developer toolkit to implement their in-app purchasing, any patent dispute should be taken up by the Cupertino firm. However, Apple's iOS Paid Apps Agreement clearly states that developers are directly responsible for "claims that any of the licensed applications and/or the end-user's possession or use of those licensed applications infringes the copyright or other intellectual property rights of any third party".

That said, when the original suit was filed, Apple filed a motion itself to intervene in the proceedings, claiming that its original licensing of the patent extends to third party developers. Lodsys, clearly, disagrees.

Certainly, this has been too much for some European developers, who have decided to withdraw their apps from US iTunes and, even, Android Market. One developer, Simon Maddox (@simonmaddox), tweeted last week: "All my apps removed from US app stores (all platforms). 0.575% of total revenue put in a spare bank account. Screw you, Lodsys."

This is rapidly turning into a patent-battle to watch...