“Under § 282 of the Patent Act of 1952, ‘[a] patent shall be presumed valid’ and ‘[t]he burden of establishing in-validity of a patent or any claim thereof shall rest on the party asserting such invalidity.’ 35 U.S.C. § 282. We consider whether § 282 requires an invalidity defense to be proved by clear and convincing evidence.”
“We hold that it does. . . . According to Microsoft, a defendant in an infringement action need only persuade the jury of an invalidity defense by a preponderance of the evidence. In the alternative, Microsoft insists that a preponderance standard must apply at least when an invalidity defense rests on evidence that was never considered by the PTO in the examination process. We reject both contentions.”
