The latest example of the danger of drafting software patent claims to include means-plus-function limitations comes from Eon Corp. IP Holdings LLC v. AT&T Mobility LLC, No. 2014-1392 (Fed. Cir. May 6, 2015). U.S. Patent No. 5,663,757 included eight "means" limitations that the district court had held indefinite under 35 U.S.C. 112. These limitations required "special programming," and were not coextensive with operation of a microprocessor. Because the claimed "means" were not described in the specification, the claims, all governed by 35 U.S.C. § 112, ¶ 6 (pre-AIA), were invalid as indefinite.
The district court had made detailed factual findings that "each of the eight claim terms at issue recited complicated, customized computer software." One "skilled in the art would need to consult algorithms outside the specification to implement the claimed functions." Further, “special code would have to be written in order to accomplish the claimed functionality.” This was more than enough to support a finding of indefiniteness, "as the defendants must only show by clear and convincing evidence that the terms at issue do not recite basic functions of a microprocessor."
Although most U.S. practitioners shy away from means-plus-function language these days, at least in software cases, applications inbound from other jurisdictions may not be drafted with U.S. means-plus-function hazards in mind. Practitioners filing applications in the U.S., whether original or claiming foreign priority, should be reluctant to include means-plus-function language in U.S. claims. I would even be reluctant to use means-plus-function language where other claims were plainly drafted without it, absent a particular reason to do so. Why invite a claim construction inquiry into whether a specification discloses -- and enables -- a particular functionality? Further, claimed algorithms should always be disclosed in as much detail as possible because it seems that some of the above reasoning could be applied to claims lacking means-plus-function language.