Legal Question in Intellectual Property in Kansas

Although I don't know the details of your case, it is quite common -- too common -- for so-called "C&D" or "cease and desist" letters to contain those types of demands. But no, you have no obligation to tell anyone anything just because an attorney demands it in a letter. If you were sued, there would be a judicial process called "discovery" that governs what they can ask for and what you must provide. A common tactic is to try to get that information as "cooperation" prior to a lawsuit, but I have never seen a case where cooperation was rewarded.

The only advice I can offer is to talk to a lawyer. I know, that can be expensive. The fact that you are posting here suggests that price is a factor for you. My guess is that if whatever you were doing was relatively small, chances are that they will leave you alone once your website is down and you are no longer using the mark. The troubling bit is, what you were doing may have been perfectly legal.

Of course, i don't know, since I don't know whose trademark was in issue, or how you were using it on your site, but there are perfectly lawful uses of words or phrases that someone owns the trademark to. "Apple", for example, is known as a TM for computers and for a record label. Don't ever assume that what you were doing was wrong just because a lawyer sent you a letter hollering that it was.

Do a bit of online research on trademark infringement. The results may either convince you that you dodged a bullet or that you took your website down for no good reason. The devil is in the details, and that's why lawyers charge so much. If you can afford one, hire one. But if not, don't be intimidated if the lawyer's letter appears to be baseless bluster.

Best of luck.