NOTE: This disposition is nonprecedential.

United States Court of Appeals 

for the Federal Circuit ______________________ 

TRUSTED KNIGHT CORPORATION,

Plaintiff-Appellant

v.

INTERNATIONAL BUSINESS MACHINES 

CORPORATION, TRUSTEER INC.,

Defendants-Appellees

______________________ 

2016-1510

______________________ 

Appeal from the United States District Court for the 

District of Delaware in No. 1:14-cv-01063-LPS, Chief 

Judge Leonard P. Stark.

______________________ 

Decided: March 7, 2017

______________________ 

PAUL R. GUPTA, Reed Smith LLP, San Francisco, CA, 

argued for plaintiff-appellant. Also represented by 

GERARD M. DONOVAN, Washington, DC; R. ERIC HUTZ,

RUDOLF EDWARD HUTZ, Wilmington, DE; JAMES

CHRISTOPHER MARTIN, Pittsburgh, PA.

DAVID A. NELSON, Quinn Emanuel Urquhart & Sullivan, LLP, Chicago, IL, argued for defendants-appellees. 
2 TRUSTED KNIGHT CORPORATION v. IBM

Also represented by JOHN THOMAS MCKEE, ALEXANDER 

RUDIS, New York, NY. 

______________________ 

Before DYK, REYNA, and STOLL, Circuit Judges.

STOLL, Circuit Judge. 

Trusted Knight Corporation appeals from a stipulated 

judgment of invalidity from the United States District 

Court for the District of Delaware following adverse 

indefiniteness rulings against its asserted patent, U.S. 

Patent No. 8,316,445. We affirm.

BACKGROUND

I.

Trusted Knight owns the ’445 patent, which generally 

discloses “systems and methods for protection against the 

operation of malware commonly used in identity-theft and 

cyber-fraud.” ’445 patent col. 1 ll. 24–26. More specifically, the ’445 patent purports to protect against a type of 

malware known as key logging.

According to the ’445 patent, key logging “is a method 

of capturing keyboard input to a computer or computing 

device” and “is a common technique for obtaining passwords and sensitive information using unauthorized 

software.” Id. at col. 1 ll. 57–60. There are many 

key-logging techniques, “including hooking various operating system Application Programming Interfaces (APIs) 

and system drivers, screen capture, and form grabbing 

and hook based keystroke logging.” Id. at col. 2 ll. 1–4. 

The ’445 patent describes in detail two types of key logging—hook-based key logging and form-grabbing key 

logging.

 The ’445 patent describes hook-based key logging as 

the insertion of a system API hook into an API stack, 

which allows the key logger to record all keystroke data 
TRUSTED KNIGHT CORPORATION v. IBM 3

passing through an operating system driver. The logger 

saves this data to a text file, which can subsequently be 

sent to malefactors at a remote location. Because this 

method of key logging indiscriminately records all of the 

keystroke data, it often results in a large volume of data 

that is burdensome to store. Additionally, this voluminous data can be “difficult to search for the purpose of 

extracting the very small percentage of data that represents credential and password information.” Id. at col. 2 

ll. 24–26. “As a result, malefactors have fine-tuned their 

malware to meet these challenges and better reduce the 

large take of useless data stolen by their malware.” Id. at 

col. 2 ll. 26–28.

One such fine-tuned version of key logging is formgrabbing key logging, which the ’445 patent describes as 

the insertion of a hook that captures form data solely from 

form data inputs. “The form information being stolen is, 

essentially, those forms used for online banking and other 

online commerce that require users to enter personal 

information, card data, passwords, reminder questions, 

and mother’s maiden names.” Id. at col. 2 ll. 31–35. For 

example, “when a user submits data to a legitimate 

banking website using web forms, a form-grabbing key 

logger that is monitoring the web browser can grab the 

submitted data by injecting a hook and hooking API 

functions within the browser.” Id. at col. 2 ll. 60–64. The 

patent further explains that sophisticated cyber criminals 

have come to prefer form-grabbing key loggers because: 

(1) they are resistant to detection and lack effective 

countermeasures; (2) they substantially reduce the volume of captured data; and (3) they capture the vast 

majority of credentials criminals want, since almost all 

credentials used for online transactions are inputted into 

a web form. 

The ’445 patent describes various prior art methods 

used to counteract key logging malware. Many of these 

methods “are available to detect and/or disable hook-
4 TRUSTED KNIGHT CORPORATION v. IBM

based key loggers.” Id. at col. 3 ll. 15–16. For example, 

“[o]ne method used is the unhooking of API’s that insert 

themselves into the API stack.” Id. at col. 3 ll. 17–19. 

The ’445 patent warns, however, that this method does 

not protect the user when the malware inserts a hook at 

the first instance in the API stack and it is also ineffective 

against form-grabbing key loggers. 

Another method works by launching a new process 

when it detects a hook-based key logger, whereby the 

keystroke data is passed through the new process and 

bypasses the keystroke-logger hook. The ’445 patent 

warns, however, that this method can cause system 

instability and can be counteracted by key loggers. 

The invention, as described in the ’445 patent specification, allegedly improves upon the prior art by preventing the actions of form-grabbing and hook-based key 

loggers in a way that “does not depend on the detection of 

malware at all.” Id. at col. 3 ll. 60–61. One embodiment 

of the invention prevents form-grabbing key logging. 

Specifically, the software: (1) identifies forms on a called 

web page; (2) connects to each form submission event; (3) 

clears all form inputs marked with INPUT or 

PASSWORD; (4) provides the user-inputted data to the 

designated receiving party, such as a bank; and (5) ensures that all password form fields are cleared from the 

API chain. 

Another embodiment of the invention prevents the actions of both hook-based and form-grabbing key loggers. 

The software hooks the kernel keyboard driver where it 

intercepts and encrypts the keystroke data received from 

the keyboard. This encrypted data is then sent to the 

intended application, such as a web browser, where the 

keystrokes are decrypted and presented to the web form 

for submission to the designated receiving entity. 

The ’445 patent has three independent claims: claims 

1, 22, and 23. Claim 1 of the ’445 patent recites:
TRUSTED KNIGHT CORPORATION v. IBM 5

1. A software program embedded in a nontransitory microprocessor-readable storage medium and executable by a microprocessor to prevent 

software key logging comprising:

a software module that inserts and executes predetermined software processes at 

a zero-ring level in an application programming interface (“API”) stack of a 

browser, said software processes including:

a process of detecting a browser 

form submission initiation call 

event at the zero-ring level, wherein the form submission initiation 

call event takes a form of an on 

Submit call or a BeforeNavigate 

call;

a process of intercepting data inputs keyed in by a user at the zero-ring level; and

a process of (1) submitting the 

keyed-in data to a designated entity through the API stack while (2) 

clearing confidential data from intercepted data at the zero-ring 

level prior to a subsequent transmission, which does not contain 

said confidential data, in response 

to the software key logging through 

the API stack to an internet communication port. 

Id. at col. 11 ll. 33–53 (disputed claim term italicized). 

Claim 22 recites:

22. A software program embedded in a nontransitory microprocessor-readable storage medi-
6 TRUSTED KNIGHT CORPORATION v. IBM

um and executable by a microprocessor to prevent 

software key logging comprising:

a software module that inserts and executes predetermined software processes at 

a zero-ring level in an application programming interface (“API”) stack of a 

browser, said software processes including:

a process of inserting an initial 

hook which works within the 0-

Ring level and prevents any other 

hooks from inserting at the 0-Ring 

level; 

a process of detecting a browser 

form submission initiation call 

event at the zero-ring level, wherein the form submission initiation 

call event takes a form of an onSubmit call or a BeforeNavigate 

call;

a process of intercepting and encrypting 

data inputs keyed in by a user at the zeroring level;

a process of passing the encrypted 

data to a 3-ring level where a hook 

inserted by a hook-based key logger;

a process of decrypting data which 

passed via the 3-ring level; and

a process of submitting the decrypted data to a designated entity 

through the API stack to an internet communication port.
TRUSTED KNIGHT CORPORATION v. IBM 7

Id. at col. 12 l. 57 – col. 13 l. 13 (disputed claim term 

italicized).1

II.

Trusted Knight sued International Business Machines Corporation and Trusteer, Inc. for infringement of 

the ’445 patent. The district court conducted a Markman 

hearing and issued a claim construction order construing 

four disputed claim terms. Trusted Knight Corp. v. Int’l 

Bus. Machs. Corp., No. 14-1063-LPS-CJB, 2015 WL 

7307134 (D. Del. Nov. 19, 2015). Relevant here, the 

district found the following disputed claim terms indefinite: (1) “in response to the software key logging through 

the API stack to an internet communication port,” recited 

in independent claims 1 and 23; and (2) “a process of 

passing the encrypted data to a 3-ring level where a hook 

inserted by a hook-based key logger,” recited in independent claim 22. Id. at *4–7. 

Following the district court’s claim construction order, 

the parties filed a stipulated final judgment of invalidity. 

Trusted Knight appeals the district court’s indefiniteness 

rulings, and we have jurisdiction under 28 U.S.C. 

§ 1295(a)(1).

DISCUSSION

On appeal, Trusted Knight argues that the district 

court erred in ruling that the claim limitation, “in response to the software key logging through the API stack 

to an internet communication port,” recited in claims 1 

and 23, is indefinite. Trusted Knight also argues that the 

district court erred in ruling that the claim limitation, “a 

process of passing the encrypted data to a 3-ring level 

 

1 We do not reproduce claim 23 because the parties 

agree that it “recites a method counterpart to claim 1.” 

Appellant Br. 16; Appellee Br. 6.
8 TRUSTED KNIGHT CORPORATION v. IBM

where a hook inserted by a hook-based key logger,” recited in claim 22, is indefinite. We address these arguments 

in turn.

I.

Pursuant to 35 U.S.C. § 112, ¶ 2, a patent specification must “conclude with one or more claims particularly 

pointing out and distinctly claiming the subject matter 

which the applicant regards as his invention.”2 The 

Supreme Court has held this definiteness provision “to 

require that a patent’s claims, viewed in light of the 

specification and prosecution history, inform those skilled 

in the art about the scope of the invention with reasonable certainty.” Nautilus, Inc. v. Biosig Instruments, Inc., 

134 S. Ct. 2120, 2129 (2014).

As the Supreme Court explained, the definiteness 

requirement “entails a ‘delicate balance.’” Id. at 2128

(quoting Festo Corp. v. Shoketsu Kinzoku Kogyo Kabushiki Co., 535 U.S. 722, 731 (2002)). On one hand, “the 

inherent limitations of language,” id. (citing Festo, 

535 U.S. at 731), must be taken into account, recognizing 

that “[s]ome modicum of uncertainty . . . is the ‘price of 

ensuring the appropriate incentives for innovation,’” id. 

(quoting Festo, 535 U.S. at 732). On the other hand, “a 

patent must be precise enough to afford clear notice of 

what is claimed, thereby ‘appris[ing] the public of what is 

still open to them.’” Id. at 2129 (alteration in original) 

(quoting Markman v. Westview Instruments, Inc., 517 U.S. 

370, 373 (1996)). “Otherwise there would be ‘[a] zone of 

 

2 Because the ’445 patent was filed before the adoption of the Leahy–Smith America Invents Act, Pub. L. No. 

112–29, § 4(e), 125 Stat. 284, 296-97 (2011), the previous 

version of § 112 governs. See AbbVie Deutschland GmbH 

& Co. KG v. Janssen Biotech, Inc., 759 F.3d 1285, 1290 

n.3 (Fed. Cir. 2014).
TRUSTED KNIGHT CORPORATION v. IBM 9

uncertainty which enterprise and experimentation may 

enter only at the risk of infringement claims.’” Id. (alteration in original) (quoting United Carbon Co. v. Binney & 

Smith Co., 317 U.S. 228, 236 (1942)).

 Here, the district court held that the claim term “in 

response to the software key logging through the API 

stack to an internet communication port” is indefinite 

because it is unclear what “in response to the software 

key logging” requires. We agree.

Trusted Knight argues that the claim limitation does 

not require responding to or detecting actual instances of 

malware on a user’s computer. This argument finds 

support in the specification, which emphasizes that “[t]he 

solution of the present invention does not depend on 

detection of malware at all.” ’445 patent at col. 3 ll. 59–

61. As the district court asked, however, “if the invention 

is not responding to malware, then what is happening 

‘[i]n response to the software key logging?’” Trusted 

Knight, 2015 WL 7307134, at *5. Trusted Knight answers 

that the claimed invention responds to the threat of 

malware: “The specification clarifies that the ‘in response 

to’ term should be read as being in response to the threat 

of key logging malware, whether detected or not, and 

whether present or not.” Appellant Br. 32. This position, 

however, is undermined by the claim language itself, 

which as the district court noted, “suggests an event 

(‘response’) triggered by another event (‘logging’).” Trusted Knight, 2015 WL 7307134, at *5. The claim limitation 

does not even refer to the “threat” or “potential presence”

of key logging; rather it refers to key logging. 

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. 

The “in response to” claim term does not “appris[e] the 

public of what is still open to them,” Nautilus, 134 S. Ct. 

at 2129 (quoting Markman, 517 U.S. at 373), and creates 
10 TRUSTED KNIGHT CORPORATION v. IBM

“[a] zone of uncertainty which enterprise and experimentation may enter only at the risk of infringement claims,”

id. (quoting United Carbon, 317 U.S. at 236). Accordingly, we hold that claims 21 and 23 of the ’445 patent are 

invalid for indefiniteness because, when read in light of 

the specification, Trusted Knight has failed to inform with 

reasonable certainty those skilled in the art about the 

scope of its invention. 

II.

Trusted Knight also argues that the disputed claim 

term, “a process of passing the encrypted data to a 3-ring 

level where a hook inserted by a hook-based key logger,” 

recited in claim 22, is not indefinite. Both parties concede 

that this claim term contains a typographical error. See 

Appellant Br. 6; Appellee Br. 2. Specifically, the claim 

term is missing a verb between “hook” and “inserted.”

“It is well-settled law that, in a patent infringement 

suit, a district court may correct an obvious error in a 

patent claim.” CBT Flint Partners, LLC v. Return Path, 

Inc., 654 F.3d 1353, 1358 (Fed. Cir. 2011) (citing I.T.S. 

Rubber Co. v. Essex Rubber Co., 272 U.S. 429, 442 (1926)). 

A district court can only correct a patent, however, if: “(1) 

the correction is not subject to reasonable debate based on 

consideration of the claim language and the specification 

and (2) the prosecution history does not suggest a different interpretation of the claims.” Novo Indus. v. Micro 

Molds Corp., 350 F.3d 1348, 1357 (Fed. Cir. 2003).

The district court held that this claim limitation was 

not amenable to correction because the correction was 

subject to reasonable debate based on consideration of the 

claim language and the specification. We agree.

Trusted Knight argues that the claim limitation can 

be corrected by inserting “is” in between “hook” and

“inserted,” so the claim limitation would read “a process of 

passing the encrypted data to a 3-ring level where a hook
TRUSTED KNIGHT CORPORATION v. IBM 11

[is] inserted by a hook-based key logger.” Such a correction, however, would suggest that the “process of passing 

the encrypted data to a 3-ring level” occurs only when a 

hook is actually inserted. But as noted above in the 

discussion of the “in response to” limitation, the specification emphasizes that the invention operates regardless of 

the presence or detection of malware. This ambiguity, 

noted by the district court, demonstrates that Trusted 

Knight’s correction to the claim language is subject to 

reasonable debate.

Indeed, other possible corrections appear to be feasible. The district court, for example, explained that it 

could correct the claim limitation by placing “could be” 

between “hook inserted,” such that the claim limitation 

would read “a process of passing the encrypted data to a 

3-ring level where a hook [could be] inserted by a hookbased key logger.” While this correction would seem to be 

consistent with the specification and Trusted Knight’s 

position that the claimed invention operates even in the 

absence of malware, it would create a different claim 

scope than Trusted Knight’s proposed correction of adding 

“is.” Thus, because the proposed construction is subject to 

reasonable debate, the disputed claim limitation is not 

amenable to correction.

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. We 

accordingly hold that claim 22 of the ’445 patent is invalid 

for indefiniteness because, when read in light of the 

specification, Trusted Knight has failed to inform with 

reasonable certainty those skilled in the art about the 

scope of its invention. 

CONCLUSION

We have considered Trusted Knight’s remaining 

arguments and determined that they lack merit. Because 

claims 1, 22, and 23 do not reasonably inform those 
12 TRUSTED KNIGHT CORPORATION v. IBM

skilled in the art about the scope of the invention with 

reasonable certainty, they are indefinite, and we affirm 

the district court’s judgment of indefiniteness. 

AFFIRMED

COSTS

Costs to Appellees.