I searched the letter, and can't find the word "patent" anywhere. Unless there is a patent involved, then the wannabe plaintif is relying on "Trade Secrets" (NDA), rather than patents to protect his turf, I'm pretty sure you can politely tell him to fuck off. (IANAL, this is not legal advice).<p>I've heard that under certain circumstances, you can write a threatening letters, just to rattle the competition. Best get a lawyer to do it, as it sounds slightly credible, and they can make sure you don't actually do anything illegal, but you can often just quote legislation and "request" people back off ... it's just a request, right? The FBI did this to wikipedia, whose legal team sent a hilarious reply.<p>It's an extremely bad idea if you have a patent they are infringing on (as direct threats will force them to counter-sue, or settle immediately, or face extra damages), but for most things you can talk as much legal smack-down as you want.