On Friday, a small Texas company called Lodsys whose key asset seems to be four heavily licensed patents covering, among other things, in-app purchases, began sending patent-infringement letters to a handful of the 40,000 developers trying to make a living selling applications in Apple's (AAPL) crowded App Store.

    Even though Apple has licensed the technologies at issue, Lodsys CEO Mark Small is claiming that every developer that uses them also owes Lodsys a cut.

    So far, the companies threatened with legal action have been relatively small and unknown. But on Tuesday, Talos Tsui, the co-founder of one of the most popular Twitter clients -- one heavily promoted on Apple's own storefront -- announced in a four-word tweet: Twitterific just got Lodsysed.

    Apple has yet to comment on the situation, which threatens to undermine a key aspect of the business model on which the App Store was constructed, but the mood of the developer community was captured by a Dutch developer's quote that was being heavily re-tweeted Tuesday morning:

    "The same patent system that has completely failed to protect the iPhone from being copied wholesale is being used to extort its developers."

    For background on the legal situation, see the Q&A posted Tuesday by FOSS Patent's Florian Mueller. For more on Mark Small, see what Patrick Igoe has dredged up.