Infringing letter

I am pretty certain that this ask was in the form of a "cease and desist" letter.  Attorneys for intellectual property holders write such letters to parties that are purportedly infringing their client's IP.  As a matter of custom, and for good reasons, these letters are usually very strongly worded.  You, the recipient of the letter, are under no obligation to comply with its demands.  However, you are very well-advised to retain the services of an attorney to advise you on what risks you may face for non-compliance.  It MAY be the case that the other side really has no legal basis for asserting their rights against you, in which case the letter simply goes in the "circular file". However, it may also be the case that the other side has a legal basis for filing suit and obtaining a judgment against you for infringing their intellectual property.  Now that you are notified of the claim of infringement, if you continue the activity and the other side really has a case, you may be held liable not only for infringement but also for WILLFUL infringement, which, depending on circumstances, may carry enhanced damages that can be claimed against you. Short answer, retain an attorney to obtain at least an initial opinion as to whether your best course is to comply with the cease and desist letter.  The advice need not be terribly expensive, perhaps one or two billable hours.