The inequitable conduct defense remains a viable defense in patent litigation today, as illustrated in four 2003 Federal Circuit decisions. Though an alleged patent infringer must establish the elements of materiality and intent for a valid inequitable conduct defense, recent Federal Circuit decisions indicate that certain factual underpinnings bearing on materiality can raise an inference of intent. To most effectively counter this inference of intent, a plausible explanation for the questioned conduct should be provided by the patentee. However, in providing such plausible explanation, the patentee runs the risk of waiving privileged communications, which in turn may result in far more intrusive and costly discovery.
Alan W. Kowalchyk and Thomas R. Johnson, The Inequitable Conduct Defense Lives On: 2003 Federal Circuit Decisions and Their Impact, 3 J. Marshall Rev. Intell. Prop. L. 189 (2004)