You have a duty to inform the U.S. Patent and Trademark Office of any information you are aware of that is material to the patentability of your invention. The duty exists for each pending claim as long as the patent application is still pending. This includes information you discover during the entire application process. Although there is no duty to search for prior art, it applies to information you and/or your patent attorney are aware of.
A failure to abide by your duty of disclosure may result in the patent being found invalid. Furthermore, if inequitable conduct is found regarding the non-disclosure of a reference, the patent and related patents may be found unenforceable. Furthermore, inequitable conduct may be a basis for awarding the accused infringer attorney fees in litigation. Inequitable conduct involves a misrepresentation, failed to disclose material information, or submittal of false information to the U.S. Patent and Trademark Office with an intent to deceive the U.S. Patent and Trademark Office.
Information may be material if it relates to your invention and:
37 C.F.R. § 1.56 details your duty of disclosure. The duty is typically fulfilled by submitting an Information Disclosure Statement. Your patent attorney can analyze any documents and other information you are aware of to determine whether a disclosure is necessary.
When you properly disclose a reference and the reference is considered by the Examiner, there is a presumption of validity of your patent over the reference if the validity of your patent is challenged in court. This means that, because the Examiner was aware of the reference during his decision to grant the patent, the opposing party must show with clear and convincing evidence that the reference invalidates the patent.