The decision is a much anticipated treatment of the «inequitable conduct standard» in US patent law. Essentially, the opinion requires a challenger to present clear and convincing evidence that the withholding of prior art was based on: (a) knowledge of its materiality; and (b) a conscious decision not to disclose it in order to deceive the US Patent & Trademark Office. In other words, rather than a «smoking gun» test (where inferences can be more readily drawn), the Court is requiring an unambiguous showing of both materiality and specific, culpable intent (rather than negligence). It is quite possible that the Supreme Court may have the final word on this matter.
Many non-US based applications have proven to be especially vulnerable to inequitable challenges due to the higher standard the US has imposed with regard to what must be disclosed in the course of seeking a patent.