LONDON - MAY 21: IBM logo on the IBM Client Centre building on May 21, 2013 in London, UK. IBM is an American multinational technology and consulting corporation.
LONDON – MAY 21: IBM logo on the IBM Client Centre building on May 21, 2013 in London, UK. IBM is an American multinational technology and consulting corporation. ()

The U.S. Court of Appeals for the Federal Circuit has upheld a Delaware judge’s ruling that a lack of clarity in claims for a patent covering anti-malware software doomed a company’s infringement case against IBM.

A three-judge panel of the appeals court on Tuesday agreed that the claims for Trusted Knight Corp.’s did not meet the “reasonable certainty” standard set out in the 2014 U.S. Supreme Court case Nautilus v. Biosig Instruments. The deficiency, the appeals court said, failed to establish the scope of Trusted Knight’s invention, rendering its patent indefinite, and thus invalid.

“After review of the relevant intrinsic evidence and the parties’ positions, we agree with the district court that the meaning of this claim limitation is not reasonably certain,” Judge Kara Farnandez Stoll wrote for the Federal Circuit in a 12-page opinion.

The nonprecedential decision affirmed a November 2015 ruling by U.S. District Chief Judge Leonard P. Stark of the District of Delaware. The parties agreed to move for entry of final judgment on the indefiniteness ruling, and Trusted Knight appealed to the Federal Circuit last January.

The Annapolis, Maryland-based security software firm had sued IBM and Boston-based Trusteer Inc. in August 2014, accusing the companies of infringing on a patent to protect against a form of malware known as key logging. According to Trusted Knight’s so-called ’445 patent, key logging is a common technique of obtaining passwords and sensitive information by capturing keyboard entries on a computer or other device.

Both Stark and Stoll identified an in a claim limitation that said the software acts “in response” to the software key logging. Trusted Knight argued that the limitation did not require the actual detection of malware on a computer, but simply the threat of malware being present.

However, Trusted Knight’s position, Stoll said, conflicted with claim language that suggested a response triggered by an event, and the lack of specificity created uncertainty among the public as to what the patent actually claimed.

Adding to the confusion, another claim was missing a verb, an obvious typographical error that both parties agreed was present.

The Federal Circuit has held that district courts may step in to correct blatant mistakes in a patent, but only when the correction is not subject to reasonable debate. Stark found that different forms of the verb “to be” could potentially be added to the claim, each one altering the scope of Trusted Knight’s claim.

On Tuesday, Stoll affirmed that finding, leaving in place the uncertain claim limitation and dealing a final blow to Trusted Knight’s infringement case.

“Thus, because the proposed construction is subject to reasonable debate, the disputed claim limitation is not amenable to correction,” she said. “Additionally, as the claim limitation stands uncorrected, it does not inform those skilled in the art about the scope of the invention with reasonable certainty.”

Attorneys for both sides were not immediately available to comment.

Quinn Emanuel Urquhart & Sullivan’s David A. Nelson, John T. McKee and Alexander Rudis represented IBM.

Paul R. Gupta, Gerard M. Donovan, R. Eric Hutz, Rudolf E. Hutz and James C. Martin of Reed Smith represented Trusted Knight.

The case was captioned Trusted Knight v. IBM.