       NOTE: This disposition is nonprecedential.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 & Sulli-
van, 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 specifical-
ly, 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 pass-
words and sensitive information using unauthorized
software.” Id. at col. 1 ll. 57–60. There are many
key-logging techniques, “including hooking various oper-
ating 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 log-
ging—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 volumi-
nous data can be “difficult to search for the purpose of
extracting the very small percentage of data that repre-
sents 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 form-
grabbing 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 vol-
ume 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 specifi-
cation, allegedly improves upon the prior art by prevent-
ing 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) en-
sures that all password form fields are cleared from the
API chain.
     Another embodiment of the invention prevents the ac-
tions 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 non-
   transitory microprocessor-readable storage medi-
   um and executable by a microprocessor to prevent
   software key logging comprising:
       a software module that inserts and exe-
       cutes predetermined software processes at
       a zero-ring level in an application pro-
       gramming interface (“API”) stack of a
       browser, said software processes includ-
       ing:
           a process of detecting a browser
           form submission initiation call
           event at the zero-ring level, where-
           in the form submission initiation
           call event takes a form of an on
           Submit call or a BeforeNavigate
           call;
           a process of intercepting data in-
           puts keyed in by a user at the ze-
           ro-ring level; and
           a process of (1) submitting the
           keyed-in data to a designated enti-
           ty through the API stack while (2)
           clearing confidential data from in-
           tercepted data at the zero-ring
           level prior to a subsequent trans-
           mission, which does not contain
           said confidential data, in response
           to the software key logging through
           the API stack to an internet com-
           munication port.
Id. at col. 11 ll. 33–53 (disputed claim term italicized).
Claim 22 recites:
   22. A software program embedded in a non-
   transitory 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 exe-
       cutes predetermined software processes at
       a zero-ring level in an application pro-
       gramming interface (“API”) stack of a
       browser, said software processes includ-
       ing:
           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, where-
           in the form submission initiation
           call event takes a form of an on-
           Submit call or a BeforeNavigate
           call;
       a process of intercepting and encrypting
       data inputs keyed in by a user at the zero-
       ring level;
           a process of passing the encrypted
           data to a 3-ring level where a hook
           inserted by a hook-based key log-
           ger;
           a process of decrypting data which
           passed via the 3-ring level; and
           a process of submitting the de-
           crypted data to a designated entity
           through the API stack to an inter-
           net 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 Ma-
chines 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 indefi-
nite: (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 independ-
ent 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 re-
sponse 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,” recit-
ed in claim 22, is indefinite. We address these arguments
in turn.
                            I.
    Pursuant to 35 U.S.C. § 112, ¶ 2, a patent specifica-
tion 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 reasona-
ble 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 Kabushi-
ki 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 adop-
tion 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. (altera-
tion 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’).” Trust-
ed 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 experimen-
tation may enter only at the risk of infringement claims,”
id. (quoting United Carbon, 317 U.S. at 236). According-
ly, 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 differ-
ent 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 correc-
tion, 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 specifica-
tion 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 feasi-
ble. 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 hook-
based 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 uncor-
rected, 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.
