<PAGE>

                                                                   EXHIBIT 10.26

          AMENDED AND RESTATED INTELLECTUAL PROPERTY SECURITY AGREEMENT

         This Amended and Restated Intellectual Property Security Agreement
(this "IP Agreement") is made as of the ____ day of January, 2004 by and between
ART TECHNOLOGY GROUP, INC., a Delaware corporation with its principal place of
business at 25 First Street, Cambridge, Massachusetts 02141("Grantor"), and
SILICON VALLEY BANK, a California-chartered bank, with its principal place of
business at 3003 Tasman Drive, Santa Clara, California 95054 and with a loan
production office located at One Newton Executive Park, Suite 200, 2221
Washington Street, Newton, Massachusetts 02462, doing business under the name
"Silicon Valley East" ("Lender").T his Amended and Restated Intellectual
Property Security Agreement amends and restates a certain Intellectual Property
Security Agreement dated as of June 13, 2002, by and between Grantor and Lender.

                                    RECITALS

         A.       Lender has agreed to make advances of money and to extend
certain financial accommodations to Grantor (the "Loan"), pursuant to a certain
Amended and Restated Loan and Security Agreement dated as of June 13, 2002,
between Grantor and Lender, as amended by a certain First Loan Modification
Agreement dated as of September 27, 2002, as further amended by a certain
Amendment dated as of October __, 2002, as further amended by a certain Second
Loan Modification Agreement dated as of December 24, 2002, as further amended by
a certain Third Loan Modification Agreement dated as of October 20, 2003, and as
further amended by a certain Fourth Loan Modification Agreement dated as of
November 26, 2003, as amended from time to time (as amended, the "Loan
Agreement"). The Loan is secured pursuant to the terms of the Loan Agreement.
Lender is willing to enter into certain financial accommodations with Grantor,
but only upon the condition, among others, that Grantor shall grant to Lender a
security interest in certain Copyrights, Trademarks, Patents, and Mask Works to
secure the obligations of Grantor under the Loan Agreement. Defined terms used
but not defined herein shall have the same meanings as in the Loan Agreement.

         B.       Pursuant to the terms of the Loan Agreement, Grantor has
granted to Lender a security interest in all of Grantor's right title and
interest, whether presently existing or hereafter acquired in, to and under all
of the Collateral (as defined therein).

         NOW, THEREFORE, for good and valuable consideration, receipt of which
is hereby acknowledged and intending to be legally bound, as collateral security
for the prompt and complete payment when due of Grantor's Indebtedness (as
defined below), Grantor hereby represents, warrants, covenants and agrees as
follows:

         1.       Grant of Security Interest. As collateral security for the
prompt and complete payment and performance of all of Grantor's present or
future indebtedness, obligations and liabilities to Lender (hereinafter, the
"Indebtedness"), including, without limitation, under the Loan Agreement,
Grantor hereby grants a security interest in all of Grantor's right, title and
interest in, to and under its intellectual property collateral (all of which
shall collectively be called the "Intellectual Property Collateral"), including,
without limitation, the following:

                  (a)      Any and all copyright rights, copyright applications,
         copyright registrations and like protections in each work or authorship
         and derivative work thereof, whether published or unpublished and
         whether or not the same also constitutes a trade secret, now or
         hereafter existing, created, acquired or held, including without
         limitation those set forth on EXHIBIT A attached hereto (collectively,
         the "Copyrights");

                  (b)      Any and all trade secrets, and any and all
         intellectual property rights in computer software and computer software
         products now or hereafter existing, created, acquired or held;

                  (c)      Any and all design rights which may be available to
         Grantor now or hereafter existing, created, acquired or held;

                  (d)      All patents, patent applications and like protections
         including, without limitation, improvements, divisions, continuations,
         renewals, reissues, extensions and continuations-in-part of the same,
         including without limitation the patents and patent applications set
         forth on EXHIBIT B attached hereto (collectively, the "Patents");

<PAGE>

                  (e)      Any trademark and servicemark rights, whether
         registered or not, applications to register and registrations of the
         same and like protections, and the entire goodwill of the business of
         Grantor connected with and symbolized by such trademarks, including
         without limitation those set forth on EXHIBIT C attached hereto
         (collectively, the "Trademarks");

                  (f)      All mask works or similar rights available for the
         protection of semiconductor chips, now owned or hereafter acquired,
         including, without limitation those set forth on EXHIBIT D attached
         hereto (collectively, the "Mask Works");

                  (g)      Any and all claims for damages by way of past,
         present and future infringements of any of the rights included above,
         with the right, but not the obligation, to sue for and collect such
         damages for said use or infringement of the intellectual property
         rights identified above;

                  (h)      All licenses or other rights to use any of the
         Copyrights, Patents, Trademarks, or Mask Works and all license fees and
         royalties arising from such use to the extent permitted by such license
         or rights, including, without limitation those set forth on EXHIBIT E
         attached hereto (collectively, the "Licenses"); and

                  (i)      All amendments, extensions, renewals and extensions
         of any of the Copyrights, Trademarks, Patents, or Mask Works; and

                  (j)      All proceeds and products of the foregoing, including
         without limitation all payments under insurance or any indemnity or
         warranty payable in respect of any of the foregoing.

         2.       Authorization and Request. Grantor authorizes and requests
that the Register of Copyrights and the Commissioner of Patents and Trademarks
record this IP Agreement.

         3.       Covenants and Warranties. Grantor represents, warrants,
covenants and agrees as follows:

                  (a)      Grantor is now the sole owner of the Intellectual
         Property Collateral, except for non-exclusive licenses granted by
         Grantor to its customers in the ordinary course of business.

                  (b)      Performance of this IP Agreement does not conflict
         with or result in a breach of any IP Agreement to which Grantor is
         bound, except to the extent that certain intellectual property
         agreements prohibit the assignment of the rights thereunder to a third
         party without the licensor's or other party's consent and this IP
         Agreement constitutes a security interest.

                  (c)      During the term of this IP Agreement, Grantor will
         not transfer or otherwise encumber any interest in the Intellectual
         Property Collateral, except for non-exclusive licenses granted by
         Grantor in the ordinary course of business or as set forth in this IP
         Agreement;

                  (d)      To its knowledge, each of the Patents is valid and
         enforceable, and no part of the Intellectual Property Collateral has
         been judged invalid or unenforceable, in whole or in part, and no claim
         has been made that any part of the Intellectual Property Collateral
         violates the rights of any third party;

                  (e)      Grantor shall promptly advise Lender of any material
         adverse change in the composition of the Collateral, including but not
         limited to any subsequent ownership right of the Grantor in or to any
         Trademark, Patent, Copyright, or Mask Work specified in this IP
         Agreement;

                  (f)      Grantor shall (i) protect, defend and maintain the
         validity and enforceability of the Trademarks, Patents, Copyrights, and
         Mask Works, (ii) use its best efforts to detect infringements of the
         Trademarks, Patents, Copyrights, and Mask Works and promptly advise
         Lender in writing of material infringements detected and (iii) not
         allow any Trademarks, Patents, Copyrights, or Mask Works to be
         abandoned, forfeited or dedicated to the public without the written
         consent of Lender, which shall not be unreasonably withheld, unless
         Grantor determines that reasonable business practices suggest that
         abandonment is appropriate.

                                       -2-

<PAGE>

                  (g)      Grantor shall promptly register the most recent
         version of any of Grantor's Copyrights, if not so already registered,
         and shall, from time to time, execute and file such other instruments,
         and take such further actions as Lender may reasonably request from
         time to time to perfect or continue the perfection of Lender's interest
         in the Intellectual Property Collateral;

                  (h)      This IP Agreement creates, and in the case of after
         acquired Intellectual Property Collateral, this IP Agreement will
         create at the time Grantor first has rights in such after acquired
         Intellectual Property Collateral, in favor of Lender a valid and
         perfected first priority security interest in the Intellectual Property
         Collateral in the United States securing the payment and performance of
         the obligations evidenced by the Loan Agreement upon making the filings
         referred to in clause (i) below;

                  (i)      To its knowledge, except for, and upon, the filing
         with the United States Patent and Trademark office with respect to the
         Patents and Trademarks and the Register of Copyrights with respect to
         the Copyrights and Mask Works necessary to perfect the security
         interests created hereunder and except as has been already made or
         obtained, no authorization, approval or other action by, and no notice
         to or filing with, any U.S. governmental authority or U.S. regulatory
         body is required either (i) for the grant by Grantor of the security
         interest granted hereby or for the execution, delivery or performance
         of this IP Agreement by Grantor in the U.S. or (ii) for the perfection
         in the United States or the exercise by Lender of its rights and
         remedies thereunder;

                  (j)      All information heretofore, herein or hereafter
         supplied to Lender by or on behalf of Grantor with respect to the
         Intellectual Property Collateral is accurate and complete in all
         material respects.

                  (k)      Grantor shall not enter into any agreement that would
         materially impair or conflict with Grantor's obligations hereunder
         without Lender's prior written consent, which consent shall not be
         unreasonably withheld. Grantor shall not permit the inclusion in any
         material contract to which it becomes a party of any provisions that
         could or might in any way prevent the creation of a security interest
         in Grantor's rights and interest in any property included within the
         definition of the Intellectual Property Collateral acquired under such
         contracts, except that certain contracts may contain anti-assignment
         provisions that could in effect prohibit the creation of a security
         interest in such contracts.

                  (l)      Upon any executive officer of Grantor obtaining
         actual knowledge thereof, Grantor will promptly notify Lender in
         writing of any event that materially adversely affects the value of any
         material Intellectual Property Collateral, the ability of Grantor to
         dispose of any material Intellectual Property Collateral or the rights
         and remedies of Lender in relation thereto, including the levy of any
         legal process against any of the Intellectual Property Collateral.

         4.       Lender's Rights. Lender shall have the right, but not the
obligation, to take, at Grantor's sole expense, any actions that Grantor is
required under this IP Agreement to take but which Grantor fails to take, after
fifteen (15) days' notice to Grantor. Grantor shall reimburse and indemnify
Lender for all reasonable costs and reasonable expenses incurred in the
reasonable exercise of its rights under this section 4.

         5.       Inspection Rights. Grantor hereby grants to Lender and its
employees, representatives and agents the right to visit, during reasonable
hours upon prior reasonable written notice to Grantor, any of Grantor's plants
and facilities that manufacture, install or store products (or that have done so
during the prior six-month period) that are sold utilizing any of the
Intellectual Property Collateral, and to inspect the products and quality
control records relating thereto upon reasonable written notice to Grantor and
as often as may be reasonably requested, but not more than once in every six (6)
months; provided, however, nothing herein shall entitle Lender access to
Grantor's trade secrets and other proprietary information.

         6.       Further Assurances; Attorney in Fact.

                  (a)      On a continuing basis, Grantor will, subject to any
prior licenses, encumbrances and restrictions and prospective licenses, make,
execute, acknowledge and deliver, and file and record in the proper filing and
recording places in the United States, all such instruments, including
appropriate financing and continuation statements and collateral

                                       -3-

<PAGE>

agreements and filings with the United States Patent and Trademarks Office and
the Register of Copyrights, and take all such action as may reasonably be deemed
necessary or advisable, or as requested by Lender, to perfect Lender's security
interest in all Copyrights, Patents, Trademarks, and Mask Works and otherwise to
carry out the intent and purposes of this IP Agreement, or for assuring and
confirming to Lender the grant or perfection of a security interest in all
Intellectual Property Collateral.

                  (b)      Grantor hereby irrevocably appoints Lender as
Grantor's attorney-in-fact, with full authority in the place and stead of
Grantor and in the name of Grantor, Lender or otherwise, from time to time in
Lender's discretion, upon Grantor's failure or inability to do so, to take any
action and to execute any instrument which Lender may deem necessary or
advisable to accomplish the purposes of this IP Agreement, including:

                           (i)      To modify, in its sole discretion, this IP
         Agreement without first obtaining Grantor's approval of or signature to
         such modification by amending Exhibit A, Exhibit B, Exhibit C, and
         Exhibit D hereof, as appropriate, to include reference to any right,
         title or interest in any Copyrights, Patents, Trademarks or Mask Works
         acquired by Grantor after the execution hereof or to delete any
         reference to any right, title or interest in any Copyrights, Patents,
         Trademarks, or Mask Works in which Grantor no longer has or claims any
         right, title or interest; and

                           (ii)     To file, in its sole discretion, one or more
         financing or continuation statements and amendments thereto, relative
         to any of the Intellectual Property Collateral without the signature of
         Grantor where permitted by law.

         7.       Events of Default. The occurrence of any of the following
shall constitute an Event of Default under this IP Agreement:

                  (a)      An Event of Default occurs under the Loan Agreement;
         or any document from Grantor to Lender; or

                  (b)      Grantor breaches any warranty or agreement made by
         Grantor in this IP Agreement.

         8.       Remedies. Upon the occurrence and continuance of an Event of
Default, Lender shall have the right to exercise all the remedies of a secured
party under the Massachusetts Uniform Commercial Code, including without
limitation the right to require Grantor to assemble the Intellectual Property
Collateral and any tangible property in which Lender has a security interest and
to make it available to Lender at a place designated by Lender. Lender shall
have a nonexclusive, royalty free license to use the Copyrights, Patents,
Trademarks, and Mask Works to the extent reasonably necessary to permit Lender
to exercise its rights and remedies upon the occurrence of an Event of Default.
Grantor will pay any expenses (including reasonable attorney's fees) incurred by
Lender in connection with the exercise of any of Lender's rights hereunder,
including without limitation any expense incurred in disposing of the
Intellectual Property Collateral. All of Lender's rights and remedies with
respect to the Intellectual Property Collateral shall be cumulative.

         9.       Indemnity. Grantor agrees to defend, indemnify and hold
harmless Lender and its officers, employees, and agents against: (a) all
obligations, demands, claims, and liabilities claimed or asserted by any other
party in connection with the transactions contemplated by this IP Agreement, and
(b) all losses or expenses in any way suffered, incurred, or paid by Lender as a
result of or in any way arising out of, following or consequential to
transactions between Lender and Grantor, whether under this IP Agreement or
otherwise (including without limitation, reasonable attorneys fees and
reasonable expenses), except for losses arising from or out of Lender's gross
negligence or willful misconduct.

         10.      Reassignment. At such time as Grantor shall completely satisfy
all of the obligations secured hereunder, Lender shall execute and deliver to
Grantor all deeds, assignments, and other instruments as may be necessary or
proper to reinvest in Grantor full title to the property assigned hereunder,
subject to any disposition thereof which may have been made by Lender pursuant
hereto.

         11.      Course of Dealing. No course of dealing, nor any failure to
exercise, nor any delay in exercising any right, power or privilege hereunder
shall operate as a waiver thereof.

                                       -4-

<PAGE>

         12.      Attorneys' Fees. If any action relating to this IP Agreement
is brought by either party hereto against the other party, the prevailing party
shall be entitled to recover reasonable attorneys fees, costs and disbursements.

         13.      Amendments. This IP Agreement may be amended only by a written
instrument signed by both parties hereto.

         14.      Counterparts. This IP Agreement may be executed in two or more
counterparts, each of which shall be deemed an original but all of which
together shall constitute the same instrument.

         15.      Law and Jurisdiction. This IP Agreement shall be governed by
and construed in accordance with the laws of the Commonwealth of Massachusetts.
GRANTOR ACCEPTS FOR ITSELF AND IN CONNECTION WITH ITS PROPERTIES,
UNCONDITIONALLY, THE NON-EXCLUSIVE JURISDICTION OF ANY STATE OR FEDERAL COURT OF
COMPETENT JURISDICTION IN THE COMMONWEALTH OF MASSACHUSETTS IN ANY ACTION, SUIT,
OR PROCEEDING OF ANY KIND, AGAINST IT WHICH ARISES OUT OF OR BY REASON OF THIS
AGREEMENT; PROVIDED, HOWEVER, THAT IF FOR ANY REASON LENDER CANNOT AVAIL ITSELF
OF THE COURTS OF THE COMMONWEALTH OF MASSACHUSETT S, GRANTOR ACCEPTS
JURISDICTION OF THE COURTS AND VENUE IN SANTA CLARA COUNTY, CALIFORNIA.

         GRANTOR AND LENDER EACH HEREBY WAIVE THEIR RESPECTIVE RIGHTS TO A JURY
TRIAL OF ANY CLAIM OR CAUSE OF ACTION BASED UPON OR ARISING OUT OF ANY OF THE
LOAN DOCUMENTS OR ANY OF THE TRANSACTIONS CONTEMPLATED THEREIN, INCLUDING
CONTRACT CLAIMS, TORT CLAIMS, BREACH OF DUTY CLAIMS, AND ALL OTHER COMMON LAW OR
STATUTORY CLAIMS. EACH PARTY RECOGNIZES AND AGREES THAT THE FOREGOING WAIVER
CONSTITUTES A MATERIAL INDUCEMENT FOR IT TO ENTER INTO THIS AGREEMENT. EACH
PARTY REPRESENTS AND WARRANTS THAT IT HAS REVIEWED THIS WAIVER WITH ITS LEGAL
COUNSEL AND THAT IT KNOWINGLY AND VOLUNTARILY WAIVES ITS JURY TRIAL RIGHTS
FOLLOWING CONSULTATION WITH LEGAL COUNSEL.

         16.      Confidentiality. In handling any confidential information,
Lender shall exercise the same degree of care that it exercises for its own
proprietary information, but disclosure of information may be made: (i) to
Lender's subsidiaries or affiliates in connection with their present or
prospective business relations with Grantor; (ii) to prospective transferees or
purchasers of any interest in the Loans; (iii) as required by law, regulation,
subpoena, or other order, (iv) as required in connection with Lender's
examination or audit; and (v) as Lender considers appropriate in exercising
remedies under this Agreement. Confidential information does not include
information that either: (a) is in the public domain or in Lender's possession
when disclosed to Lender, or becomes part of the public domain after disclosure
to Lender; or (b) is disclosed to Lender by a third party, if Lender does not
know that the third party is prohibited from disclosing the information.

                                       -5-

<PAGE>

         EXECUTED as a sealed instrument under the laws of the Commonwealth of
Massachusetts on the day and year first written above.

ADDRESS OF GRANTOR:                            GRANTOR:

25 First Street, Cambridge, Massachusetts      ART TECHNOLOGY GROUP, INC.

                                               By:    /s/ Edward Terino
                                                     ---------------------------
                                               Name:  Edward Terino
                                                     ---------------------------
                                               Title: Chief Financial Officer
                                                     ---------------------------

                                       -6-

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         Exhibit "A" attached to that certain Amended and Restated Intellectual
Property Security Agreement dated ________________, 2004.

                                   EXHIBIT "A"

                                   COPYRIGHTS

                         SCHEDULE A - ISSUED COPYRIGHTS

COPYRIGHT                        REGISTRATION                      DATE OF
DESCRIPTION                         NUMBER                         ISSUANCE

                                      NONE

                  SCHEDULE B - PENDING COPYRIGHT APPLICATIONS

                                                                 FIRST DATE
COPYRIGHT         APPLICATION       DATE OF        DATE OF       OF PUBLIC
DESCRIPTION         NUMBER          FILING        CREATION      DISTRIBUTION

                                      NONE

            SCHEDULE C - UNREGISTERED COPYRIGHTS (Where No Copyright
                             Application is Pending)

<TABLE>
<CAPTION>
                                                       DATE AND RECORDATION NUMBER
                                                      OF IP AGREEMENT WITH OWNER OR
                                                              ORIGINAL
                                                             GRANTOR IF                 ORIGINAL AUTHOR
                                                            AUTHOR OR OWNER               OR OWNER OF
                                FIRST DATE                   OF COPYRIGHT                  COPYRIGHT IS
COPYRIGHT         DATE OF           OF                      IS DIFFERENT                 DIFFERENT ROM
DESCRIPTION      CREATION      DISTRIBUTION                 FROM GRANTOR                    GRANTOR
------------     --------      ------------                 ------------                    -------
<S>              <C>           <C>                    <C>                               <C>
</TABLE>

                              ALL DYN AMO VERSIONS

                                       -7-

<PAGE>

Exhibit "B" attached to that certain Amended and Restated Intellectual Property
Security Agreement dated _______________, 2004.

                                  EXHIBIT "B"

                                     PATENTS

PATENT
DESCRIPTION   DOCKET NO. COUNTRY      SERIAL NO.        FILING DATE STATUS

                                      NONE

                                       -8-

<PAGE>

Exhibit "C" attached to that certain Amended and Restated Intellectual Property
Security Agreement dated _________________, 2004.

                                  EXHIBIT "C"

                                   TRADEMARKS

TRADEMARK
DESCRIPTION       COUNTRY            SERIAL NO.           REG. NO         STATUS

                              SEE ATTACHED EXHIBIT

                                      -9-

<PAGE>

Exhibit "D" attached to that certain Amended and Restated Intellectual Property
Security Agreement dated _______2004.

                                   EXHIBIT "D"

                                   MASK WORKS

 MASK WORK
DESCRIPTION             COUNTRY        SERIAL NO.         REG. NO         STATUS

                                      NONE

                                      -10-

<PAGE>

Exhibit "E" attached to that certain Amended and Restated Intellectual Property
Security Agreement dated _____________, 2004.

                                   EXHIBIT "E"

                                    LICENSES

                              SEE ATTACHED EXHIBIT

                                      -11-