Suing Open Source Startups - A New Scam?
If they won't even identify their patent numbers then they are obviously full of crap and just trying to hold you up for money. However, you can look up patents yourself online at http://www.uspto.gov and search by things like the name and city/state of the inventor or assignee. You could then see if the company even has any patents, and if they do if there is any merit at all to their claims your software infringes on them. That information should be very useful to your lawyer in advising you on whether you can just blow them off or not.