On Thursday June 9, 2011, the Supreme Court, by an 8-0 decision, held that a party challenging validity of a patent must prove invalidity by clear and convincing evidence rather than by a preponderance of evidence under 35 U.S.C. §282. The Court’s holding refused Microsoft’s proposal to establish a lower evidentiary standard for invalidating a patent based on prior art that an examiner did not review during prosecution of the patent-in-suit.

In Microsoft, the plaintiffs (“i4i”) asserted U.S. Patent No. 5,787,449 (“the ‘449 patent”), relating to editing mark-up language documents, such as those created using extensible mark-up language or XML, against Microsoft’s Word products. Specifically, i4i alleged that Microsoft Word® users infringe the ‘449 patent when they use the application to open files containing custom XML.