Yesterday, we received word from Rob Gloess of Computer LogicX, the company behind the Mix & Mash and Mix & Mash LITE applications for iOS, that he had received legal documents threatening a patent lawsuit over the use of an "upgrade" button in the lite version of his application linking users to the App Store where they could purchase the full version.

Our app, Mix & Mash, has the common model of a limited free, lite, version and a full version that contains all the features. We were told that the button that users click on to upgrade the app, or rather link to the full version on the app store was in breach of US patent no 7222078, we couldn't believe it, the upgrade button!?!

The patent in question was filed in December 2003 as part of series of continuations on earlier patent applications dating back to 1992. The patent is credited to Dan Abelow, who sold his extensive portfolio of patents to holding firm Lodsys in 2004. Lodsys is indeed the company issuing the threats of a lawsuit regarding the patent in question.

Computer LogiX is not the only App Store developer being hit with threats of a lawsuit, as Cult of Mac notes that James Thomson, the developer behind PCalc, has been hit with a similar notice. While Thomson has not identified the company pursuing the action, the timing and details suggest that Lodsys is also responsible.

"Just got hit by very worrying threat of patent infringement lawsuit for using in-app purchase in PCalc Lite. Legal docs arrived via fedex," Thomson wrote. "No idea what to do... They seem to be effectively claiming the rights to in-app purchase, but going after me, not Apple."

Thomson has reached out to Apple for guidance, and it remains to be seen how things will play out. According to Thomson, the patent holder is demanding that a license be negotiated within 21 days or a lawsuit will be filed.

At least one other developer is cited in the report as receiving similar notice of patent infringement, and that total will almost certainly grow as awareness of the situation increases, so it appears that the action is a relatively widespread one by Lodsys.

Notably, Lodsys cited the same patent, among others, when it filed suit against a host of major printer companies earlier this year.