I'm reaching out to the collective experience of my readers. Today I received a letter from a US attorney that claims that Bla-bla List infringes on US Patent No. 6,917,941.

Bla-bla List has just been an experiment for me with Rich Internet Applications. It has always been an open-source effort and I made it available as a free service to see how well it would fare out in the wild. Since this service never generated any revenue for me, paying for a lawyer to dig into this is something that I'd like the avoid (though maybe I can't).

Has anyone here ever had to defend himself again such a claim? Does the software being open-source or the service being free make any difference?

Thanks for any help or recommendations that you can give me.

update: people have asked me for the lawyer's letter and the claim, I scanned it and you can download it as a 1MB PDF from http://blablalist.com/ca-08-437.pdf or browse through it online at http://www.docstoc.com/docs/document-preview.aspx?doc_id=953027

update 2: seems I'm not alone in this, they have sued about any list application out there : http://www.techcrunch.com/2008/07/17/channel-intelligence-sues-just-about-everyone-who-offers-wishlists/