The case originated at the US District Court for the District of Delaware, where Trusted Knight sued IBM for patent infringement.
According to the patent, the software improves upon other anti-malware software by preventing form grabbing and hook-based keyloggers in a way that “does not depend on the detection of malware at all”.
But the district court ruled in January 2016 that a claim limitation, “in response to the software key logging through the API stack to an internet communication port”, was indefinite.
The US Supreme Court held in Nautilus v Biosig Instruments that a patent is indefinite “if its claims, read in light of the specification delineating the patent, and the prosecution history, fail to inform, with reasonable certainty, those skilled in the art about the scope of the invention”.
The Federal Circuit ruled on 7 March that the term “in response to” does not “apprise the public of what is still open to them”, and creates “a zone of uncertainty which enterprise and experimentation may enter only at the risk of infringement claims”.
“Trusted Knight has failed to inform with reasonable certainty those skilled in the art about the scope of its invention”, the Federal Circuit said.