The U.S. Court of Appeals for the Federal Circuit released its en banc decision in Therasense (PDF). The majority held that the defendant must prove the applicant misrepresented or omitted material with a specific intent to deceive the patent office to be successful with an inequitable conduct defence.
The court wrote (at page 19):
To prevail on the defense of inequitable conduct, the accused infringer must prove that the applicant misrepresented or omitted material information with the specific intent to deceive the PTO. Id. The accused infringer must prove both elements—intent and materiality—by clear and convincing evidence.