Document:

<PAGE>

                                                                     Exhibit 4.2

                          REGISTRATION RIGHTS AGREEMENT
                          -----------------------------

     THIS REGISTRATION RIGHTS AGREEMENT (this "Agreement") is entered into as of
                                               ---------
May 6, 2002, by and between DoubleClick Inc., a Delaware corporation (the
"Holder"), and NetRatings, Inc., a Delaware corporation (the "Company").
 ------                                                       -------

                              W I T N E S S E T H:
                              - - - - - - - - - -

     WHEREAS, the Company and the Holder are parties to that certain Asset
Purchase Agreement, dated as of May 6, 2002 (the "Asset Purchase Agreement")
                                                  ------------------------
pursuant to which (among other things) the Company will issue and sell to the
Holder 505,739 shares (the "Shares") of the Company's common stock, par value
                            ------
$0.001 per share (the "Company Common Stock");
                       --------------------

     WHEREAS, the parties desire to enter into this Agreement in order to, among
other things, set forth the rights of the Holder to cause the Company to
register the Shares with the Securities and Exchange Commission (the "SEC") for
                                                                      ---
resale pursuant to the Securities Act of 1933, as amended (the "Securities
                                                                ----------
Act"); and
---

     WHEREAS, the execution and delivery of this Agreement is a condition
precedent to the parties' obligations under the Asset Purchase Agreement.

     NOW, THEREFORE, in consideration of the mutual promises, agreements and
covenants hereinafter set forth, the parties hereto hereby agree as follows:

     1.   Definitions.
          -----------

     As used in this Agreement, the following terms shall have the respective
meanings set forth below:

     "Agreement" has the meaning set forth in the preamble to this Agreement.
      ---------

     "Asset Purchase Agreement" has the meaning set forth in the recitals to
      ------------------------
this Agreement.

     "Company" has the meaning set forth in the preamble to this Agreement.
      -------

     "Company Common Stock" has the meaning set forth in the recitals to this
      --------------------
Agreement.

     "Effectiveness Deadline" has the meaning set forth in Section 2 of this
      ----------------------
Agreement.

     "Exchange Act" means the Securities Exchange Act of 1934, as amended.
      ------------

     "Filing Deadline" has the meaning set forth in Section 2 of this Agreement.
      ---------------

     "First Sale Date" has the meaning set forth in Section 9 of this Agreement.
      ---------------

     "Holder" has the meaning set forth in the preamble to this Agreement.
      ------

<PAGE>

     "Holder Subsidiary" has the meaning set forth in Section 9 of this
      -----------------
Agreement.

     "Indemnified Person" has the meaning set forth in Section 8 of this
      ------------------
Agreement.

     "Indemnifying Person" has the meaning set forth in Section 8 of this
      -------------------
Agreement.

     "Losses" has the meaning set forth in Section 8 of this Agreement.
      ------

     "NASDAQ" means the National Association of Securities Dealers Automated
      ------
Quotation Service.

     "Notice" has the meaning set forth in Section 8 of this Agreement.
      ------

     "Person" means an individual, corporation, partnership, association, trust
      ------
or other entity or organization, including a government or political subdivision
or an agency or instrumentality thereof.

     "Prospectus" has the meaning set forth in Section 3 of this Agreement.
      ----------

     "register" (and "registered" and "registration") shall mean a registration
      --------        ----------       ------------
effected by preparing and filing the Registration Statement in compliance with
the Securities Act with the SEC, and the declaration or ordering of the
effectiveness by the SEC of such Registration Statement.

     "Registrable Securities" means (a) the Shares issued and sold to Holder
      ----------------------
under the Asset Purchase Agreement and (b) any Company Common Stock issued or
issuable with respect to the Shares in connection with any conversion, stock
split, stock dividend, recapitalization or similar event of the Company.

     "Registration Default" has the meaning set forth in Section 2 of this
      --------------------
Agreement.

     "Registration Expenses" means all expenses incurred by the Company in
      ---------------------
complying with its obligations hereunder, including, without limitation, all
registration, qualification and filing fees (including SEC filing fees),
printing expenses, escrow fees, fees and disbursements of counsel and
independent public auditors for the Company, blue sky fees and expenses (if
any), the expense of any special audits incident to or required by any such
registration.

     "Registration Statement" has the meaning set forth in Section 2 of this
      ----------------------
Agreement.

     "SEC" has the meaning set forth in the recitals to this Agreement.
      ---

     "Securities Act" has the meaning set forth in the recitals to this
      --------------
Agreement.

     "Seller Registrable Securities" has the meaning set forth in Section 2 of
      -----------------------------
this Agreement.

     "Selling Expenses" shall mean all selling commissions and stock transfer
      ----------------
taxes applicable to the Registrable Securities sold by the Holder.

     "Shares" has the meaning set forth in the recitals to this Agreement.
      ------

                                        2

<PAGE>

     "Suspension Notice" has the meaning set forth in Section 4 of this
      -----------------
Agreement.

     "Transfer" has the meaning set forth in Section 9 of the Agreement.
      --------

     2.   Registration of the Registrable Securities; Liquidated Damages.
          --------------------------------------------------------------

     (a) As soon as practicable after the date hereof but in no event later than
35 calendar days after the date hereof (such 35th day, the "Filing Deadline"),
                                                            ---------------
the Company shall file with the SEC a registration statement on Form S-3
pursuant to Rule 415 under the Securities Act (the "Registration Statement"),
                                                    ----------------------
relating to all Registrable Securities then held by the Holder, and shall use
its commercially reasonable efforts to cause such Registration Statement to
become effective as soon as practicable thereafter but in no event later than
120 calendar days after the Closing Date (such 120th day, the "Effectiveness
                                                               -------------
Deadline").
--------

     (b) The Company shall use commercially reasonable efforts to keep the
Registration Statement continuously effective, supplemented and amended to the
extent necessary to ensure that it is available for sales of Registrable
Securities by the Holder, and to ensure that it conforms with the requirements
of this Agreement, the Securities Act and the policies, rules and regulations of
the SEC as announced from time to time, until the earliest of (i) the date on
which all Registrable Securities covered by such Registration Statement have
been sold pursuant thereto and (ii) the date on which all Registrable Securities
may be sold by the Holder pursuant to Rule 144(k) under the Securities Act (or
any successor rule or regulation).

     (c) If, due to a breach of Section 2(a) or 2(b) hereof, the Registration
Statement

          (i) is not filed with the SEC on or prior to the Filing Deadline,

          (ii) has not been declared effective by the SEC on or prior to the
          Effectiveness Deadline, or

          (iii) is filed with the SEC and declared effective, but shall
          thereafter cease to be effective or fail to be usable for its intended
          purpose without being succeeded immediately by a post-effective
          amendment to such Registration Statement that cures such failure and
          that is itself declared effective within five (5) trading days of
          filing such post-effective amendment to the Registration Statement
          (each such event referred to in clauses (i) through (iii), a
          "Registration Default"),
           --------------------

then, in each such event, the Company hereby agrees to pay to the Holder
liquidated damages in cash in an amount equal to $0.03 per week per share of
Common Stock of Registrable Securities held by the Holder which during the
period(s) of such Registration Default be permitted to be sold by the Holder
pursuant to the lock-up provisions of Section 9 (such shares, "Sellable
                                                               --------
Registrable Securities"), for each week or portion thereof that a Registration
----------------------
Default continues for the first 90-day period immediately following the
occurrence of such Registration Default; provided that the amount of the
liquidated damages shall increase by an additional $0.015 per week per share of
Sellable Registrable Securities held by the Holder with respect to each
subsequent 90-day period until all Registration Defaults have been cured, up to
a maximum amount of liquidated damages of $0.06 per week per share of Sellable
Registrable Securities held by the Holder; and provided further that the Company
shall in no event be required to pay

                                        3

<PAGE>

liquidated damages for more than one Registration Default at any given time. All
accrued liquidated damages shall be paid to the Holder in full, in cash by wire
transfer of immediately available funds to an account designated by the Holder,
on the first calendar day of every quarter during which an obligation to pay
liquidated damages remains unsatisfied; provided that all outstanding liquidated
damages shall nonetheless be paid in full upon the curing of such Registration
Default. Notwithstanding the fact that any Registrable Securities for which
liquidated damages are due cease to be Registrable Securities (by virtue of
their being sold pursuant to the Registration Statement subsequent to the cure
of a Registration Default or otherwise), all obligations of the Company to pay
liquidated damages with respect thereto shall survive until such time as all
such obligations shall have been satisfied in full.

     3. Company Procedures. In connection with the Registration Statement, the
        ------------------
Company shall:

     (a) Use commercially reasonable efforts to effect such registration to
permit the sale of the Registrable Securities being sold in accordance with the
intended method or methods of distribution thereof (as indicated in the
information furnished to the Company pursuant to Section 4 hereof, within the
time periods and otherwise in accordance with the provisions of this Agreement,
and pursuant thereto the Company will prepare and file with the SEC the
Registration Statement under the Securities Act. The Company shall not include
in the Registration Statement any securities other than the Registrable
Securities.

     (b) Notwithstanding the foregoing, upon the occurrence of any event that
would cause the Registration Statement or the prospectus included therein (the
"Prospectus") (i) to contain an untrue statement of a material fact or omit to
 ----------
state any material fact necessary to make the statements therein not misleading
or (ii) not to be effective and usable for resale of Registrable Securities
during the period required by this Agreement, the Company shall file promptly an
appropriate amendment to the Registration Statement (and appropriate supplement
to the Prospectus) curing such defect, and, if SEC review is required, use
commercially reasonable efforts to cause such amendment to be declared effective
as soon as practicable.

     (c) Prepare and file with the SEC such amendments and post-effective
amendments to the Registration Statement and take all such other actions as may
be necessary to keep the Registration Statement continuously effective for the
period specified in Section 2(b) of this Agreement, cause the Prospectus to be
supplemented by any required Prospectus supplement, and as so supplemented to be
filed pursuant to Rule 424 under the Securities Act, and to comply fully with
Rules 424, 430A and 462, as applicable, under the Securities Act in a timely
manner; and comply with the provisions of the Securities Act with respect to the
disposition of all Registrable Securities covered by the Registration Statement
during the applicable period in accordance with the intended method or methods
of distribution by the Holder (as indicated in the information furnished to the
Company pursuant to Section 4 hereof).

     (d) Advise the Holder promptly and, if requested by such Persons, confirm
such advice in writing, (i) when the Prospectus or any Prospectus supplement or
post-effective amendment has been filed, and, with respect to the Registration
Statement or any post-effective amendment thereto, when the same has been
declared effective by the SEC, (ii) of any request by the SEC for amendments to
the Registration Statement or amendments or supplements to the

                                        4

<PAGE>

Prospectus or for additional information relating thereto, (iii) of the issuance
by the SEC of any stop order suspending the effectiveness of the Registration
Statement under the Securities Act or of the suspension by any state securities
commission of the qualification of the Registrable Securities for offering or
sale in any jurisdiction, or the initiation of any proceeding for any of the
preceding purposes, (iv) of the existence of any fact or the happening of any
event that makes any statement of a material fact made in the Registration
Statement, the Prospectus, any amendment or supplement thereto or any document
incorporated by reference therein untrue, or that requires the making of any
additions to or changes in the Registration Statement in order to make the
statements therein not misleading, or that requires the making of any additions
to or changes in the Prospectus in order to make the statements therein, in the
light of the circumstances under which they were made, not misleading. If at any
time the SEC shall issue any stop order suspending the effectiveness of the
Registration Statement, or any state securities commission or other regulatory
authority shall issue an order suspending the qualification or exemption from
qualification of the Registrable Securities under state securities or blue sky
laws, the Company shall use commercially reasonable efforts to obtain the
withdrawal or lifting of such order at the earliest possible time.

     (e) Subject to Section 3(b) of this Agreement, if any fact or event
contemplated by Section 3(d)(iv) above shall exist or have occurred, prepare a
supplement or post-effective amendment to the Registration Statement or related
Prospectus or any document incorporated therein by reference or file any other
required document so that, as thereafter delivered to the purchasers of
Registrable Securities, the Prospectus will not contain an untrue statement of a
material fact or omit to state any material fact necessary to make the
statements therein, in the light of the circumstances under which they were
made, not misleading.

     (f) Furnish to the Holder such reasonable number of copies of the
Registration Statement, preliminary Prospectus, final Prospectus and such other
documents as such Persons may reasonably request in order to facilitate the
public offering of the Registrable Securities.

     (g) Use its best efforts to register and qualify the Registrable Securities
covered by the Registration Statement under the securities laws of such
jurisdictions as shall be reasonably appropriate for the distribution of the
Registrable Securities covered by the Registration Statement; provided that the
Company shall not be required in connection therewith or as a condition thereto
to qualify to do business or to file a general consent to service of process in
any such jurisdiction.

     (h) Cause all Registrable Securities registered pursuant to the
Registration Statement to be (i) listed on each securities exchange on which the
Company Common Stock is then listed or (ii) authorized for quotation on the
NASDAQ National Market System if the Company Common Stock is then so authorized
for quotation.

     (i) Provide a transfer agent and registrar for all Registrable Securities
registered pursuant to the Registration Statement and a CUSIP number for all
such Registrable Securities, in each case not later than the date that the SEC
has declared the Registration Statement effective.

     4.   Holder Procedures.
          -----------------

                                        5

<PAGE>

     (a) The Holder shall, upon receipt of the notice referred to in Section
3(d)(iii) or any notice from the Company of the existence of any fact of the
kind described in Section 3(d)(iv) of this Agreement (in each case, a
"Suspension Notice"), the Holder will forthwith discontinue disposition of the
 -----------------
Registrable Securities pursuant to the applicable Registration Statement until
(i) the Holder has received copies of the supplemented or amended Prospectus
contemplated by Section 3(e) of this Agreement, or (ii) such Holder is advised
in writing by the Company that the use of the Prospectus may be resumed, and has
received copies of any additional or supplemental filings that are incorporated
by reference in the Prospectus. Upon the Holder receiving a Suspension Notice,
the Holder will either (i) destroy any Prospectuses, other than permanent file
copies, then in such Holder's possession which have been replaced by the Company
with more recently dated Prospectuses or (ii) deliver to the Company (at the
Company's expense) all copies, other than permanent file copies, then in such
Holder's possession of the Prospectus covering such Registrable Securities that
was current at the time of receipt of the Suspension Notice.

     (b) In connection with the filing of the Registration Statement, the Holder
shall furnish to the Company in writing, (i) the information specified in Item
507 and 508 of Regulation S-K, as applicable, of the Securities Act for use in
connection with the Registration Statement or any Prospectus and (ii) any
additional information required to be disclosed in order to make the information
previously furnished to the Company by such Holder not materially misleading.

     5. Expenses of Registration. All Registration Expenses shall be borne by
        ------------------------
the Company and all Selling Expenses relating to Registrable Securities
registered on behalf of the Holder shall be borne by the Holder.

     6. Rule 144 Reporting. With a view to making available the benefits of the
        ------------------
rules and regulations of the SEC which may at any time permit the sale of the
Registrable Securities to the public without registration, the Company agrees to
use best efforts to:

     (a) make and keep public information available, as those terms are
understood and defined in Rule 144 under the Securities Act, for so long as the
Company remains subject to the reporting requirements of the Securities Act or
the Exchange Act;

     (b) file with the SEC in a timely manner all reports and other documents
required of the Company under the Securities Act and the Exchange Act, for so
long as the Company remains subject to such reporting requirements; and

     (c) so long as the Holder owns any Registrable Securities, furnish to the
Holder forthwith upon request, a written statement by the Company as to its
compliance with the reporting requirements of Rule 144 under the Securities Act,
a copy of the most recent annual or quarterly report of the Company, and such
other reports and documents of the Company and other information in the
possession of, or reasonably obtainable by, the Company as the Holder may
reasonably request in availing itself of any rule or regulation of the
Commission allowing the Holder to sell any Registrable Securities pursuant to an
exemption from registration.

                                        6

<PAGE>

     7. Termination of Registration Rights. The registration rights granted to
        ----------------------------------
the Holder pursuant to this Agreement shall terminate from and after the time
when all of the Registrable Securities held by the Holder could be sold pursuant
to Rule 144(k) under the Securities Act (or any successor rule or regulation).

     8. Indemnification.
        ---------------

     (a) The Company agrees to indemnify and hold harmless the Holder, its
directors, its officers and each Person, if any, who controls the Holder (within
the meaning of Section 15 of the Securities Act and Section 20 of the Exchange
Act), from and against any and all losses, claims, damages, liabilities,
judgments, (including, without limitation, reimbursement for any legal or other
expenses incurred in connection with investigating or defending any matter,
including any action that could give rise to any such losses, claims, damages,
liabilities or judgments (collectively, "Losses")) caused by any untrue
                                         ------
statement or alleged untrue statement of a material fact contained in the
Registration Statement, preliminary Prospectus or final Prospectus (or any
amendment or supplement thereto) or caused by any omission or alleged omission
to state therein a material fact required to be stated therein or necessary to
make the statements therein not misleading or caused by any violation of the
Securities Act or the Exchange Act; provided however, that the Company does not
agree to indemnify and hold harmless the Holder, its directors, its officers and
each Person, if any who controls the Holder (within the meaning of Section 15 of
the Securities Act and Section 20 of the Exchange Act), insofar as such Losses
are caused by an untrue statement or omission or alleged untrue statement or
omission that is based upon information relating to the Holder and furnished by
the Holder in writing pursuant to Section 4(b) of this Agreement.

     (b) The Holder agrees to indemnify and hold harmless the Company and its
directors and officers, and each person, if any, who controls (within the
meaning of Section 15 of the Securities Act or Section 20 of the Exchange Act)
the Company, from and against any Losses caused by any untrue statement or
alleged untrue statement of a material fact contained in the Registration
Statement, preliminary Prospectus or final Prospectus (or any amendment or
supplement thereto) or caused by any omission or alleged omission to state
therein a material fact required to be stated therein or necessary to make the
statements therein not misleading or caused by any violation of the Securities
Act or the Exchange Act, but only to the extent that such Losses are caused by
an untrue statement or omission or alleged untrue statement or omission that is
based upon (and in conformity with) information relating to the Holder and
furnished by the Holder in writing pursuant to Section 4(b) of this Agreement;
provided, however, that in no event shall the Holder, its directors, its
officers or any Person, if any, who controls the Holder be (in the aggregate)
liable or responsible for Losses in an amount in excess of the net proceeds
actually received by the Holder in the sale of its Registrable Securities
pursuant to the Registration Statement.

     (c) In the event that any Person shall incur or suffer any Losses in
respect of which indemnification may be sought hereunder, such Person (the
"Indemnified Person") may assert a claim for indemnification by providing
 ------------------
written notice to the party from whom indemnification is being sought (the
"Indemnifying Person"), stating the amount of Losses, if known, and the nature
 -------------------
and basis of such claim (the "Notice"). In the case of Losses that arise or may
                              ------
arise by reason of any third-party claim, promptly after receipt by an
Indemnified Person of written

                                        7

<PAGE>

notice of the assertion of any claim or the commencement of any action with
respect to any matter in respect of which indemnification may be sought
hereunder, the Indemnified Person shall give Notice to the Indemnifying Person
and shall thereafter keep the Indemnifying Person reasonably informed with
respect thereto; provided that failure of the Indemnified Person to give the
Indemnifying Person prompt notice as provided herein shall not relieve the
Indemnifying Person of any of its obligations hereunder, except to the extent
that the Indemnifying Person is materially prejudiced by such failure. In case
any such claim is made or action is brought against any Indemnified Person, the
Indemnifying Person shall be entitled to assume the defense thereof, by written
notice of its intention to do so to the Indemnified Person within 30 days after
receipt of the Notice. If the Indemnifying Person shall assume the defense of
such claim or action, it shall have the right to settle such claim or action;
provided, however, that it shall not settle such claim or action without the
prior written consent of the Indemnified Person (which consent shall not be
unreasonably withheld or delayed) if such settlement (i) does not include as an
unconditional term thereof the giving by the claimant or the plaintiff of a
release of the Indemnified Person from all liability with respect to such claim
or action or (ii) involves the imposition of equitable remedies or the
imposition of any obligations on such Indemnified Person other than financial
obligations for which such Indemnified Person will be indemnified in full
hereunder. As long as the Indemnifying Person is contesting any such claim or
action in good faith, the Indemnified Person shall not pay or settle such claim
or action. Following delivery of notice of its intention to assume the defense
of any claim or action hereunder, the Indemnifying Person shall not be liable
hereunder for any legal or other expenses subsequently incurred by the
Indemnified Person in connection with the defense thereof; provided that if the
defendants in any action shall include both an Indemnifying Person and any
Indemnified Person and such Indemnified Person shall have reasonably concluded
that counsel selected by the Indemnifying Person has a conflict of interest
because of the availability of different or additional defenses to such
Indemnified Person, such Indemnified Person shall have the right to separate
counsel to participate in the defense of such action on its behalf, at the
expense of the Indemnifying Person; provided, however, that the Indemnifying
Person shall not be obligated to pay the expenses of more than one separate
counsel for all Indemnified Parties, taken together, in connection with a
particular Loss. If the Indemnifying Person shall fail to notify the Indemnified
Person of its desire to assume the defense of any claim or action within the
prescribed period of time, or shall notify the Indemnified Person that it will
not assume the defense thereof, then the Indemnified Person may assume the
defense of such claim or action, in which event it may do so acting in good
faith, and the Indemnifying Person shall be bound by any determination made in
any such action, provided, however, that the Indemnified Person shall not be
permitted to settle any such action without the consent of the Indemnifying
Person, which consent shall not be unreasonably withheld or delayed. No such
determination or settlement shall affect the right of the Indemnifying Person to
dispute the Indemnified Person's claim for indemnification hereunder. The
Indemnifying Person shall be permitted to participate in the defense of such
claim or action and to employ counsel at its own expense. If the Indemnifying
Person chooses to assume the defense of any claim or action pursuant hereto, the
Indemnified Person shall cooperate in such defense, which cooperation shall
include the retention and the provision to the Indemnifying Person of records
and information which are reasonably relevant to such defense, and making
employees available on a mutually convenient basis to provide additional
information and explanation of any materials provided hereunder, including
providing such employees to serve as witnesses.

                                        8

<PAGE>

     (d) If the indemnification provided for in this Section 8 is held by a
court of competent jurisdiction to be unavailable to, or unenforceable for any
reason by, an Indemnified Person with respect to any Loss, then the Indemnifying
Person, in lieu of indemnifying such Indemnified Person hereunder, shall
contribute to the amount paid or payable by such Indemnified Person as a result
of such Loss in such proportion as is appropriate to reflect the relative fault
of the Indemnifying Person, on the one hand, and of the Indemnified Person, on
the other, in connection with the statements or omissions that resulted in such
Loss as well as any other relevant equitable considerations. The relative fault
of the Indemnifying Person and of the Indemnified Person shall be determined by
reference to, among other things, whether the untrue or alleged untrue statement
of a material fact or the omission to state a material fact relates to
information supplied by the Indemnifying Person or by the Indemnified Person and
the parties' relative intent, knowledge, access to information, and opportunity
to correct or prevent such statement or omission. In no event shall any
contribution by the Holder under this Section 8(d), together with any amounts
paid by the Holder under Section 8(b), exceed the net proceeds actually received
by the Holder in the sale of its Registrable Securities pursuant to the
Registration Statement.

     9. Lock-up. The Holder agrees that following the date hereof it will not
        -------
sell, transfer, dispose of, pledge or hypothecate any Registrable Securities
(any such transaction, a "Transfer") except as set forth below:
                          --------

     (a) It will not Transfer any Registrable Securities until the date that is
the earlier of (i) the date on which the SEC declares the Registration Statement
effective, and (ii) the Effectiveness Deadline (such earlier date, the "First
                                                                        ----
Sale Date").
---------

     (b) Following the First Sale Date, the Holder may Transfer Registrable
Securities in a cumulative aggregate amount up to the limits as set forth below:

<TABLE>
At any time following:                                     Up to:
<S>                                                        <C>
the date hereof                       ..................   7.69% of all Registrable Securities

the 30th day after the date hereof    ..................   17.95% of all Registrable Securities

the 60th day after the date hereof    ..................   28.21% of all Registrable Securities

the 90th day after the date hereof    ..................   38.46% of all Registrable Securities

the 120th day after the date hereof   ..................   48.72% of all Registrable Securities

the 150th day after the date hereof   ..................   58.97% of all Registrable Securities

the 180th day after the date hereof   ..................   69.23% of all Registrable Securities

the 210th day after the date hereof   ..................   79.49% of all Registrable Securities

the 240th day after the date hereof   ..................   89.74% of all Registrable Securities
</TABLE>

                                        9

<PAGE>

<TABLE>
<S>                                   <C>                  <C>
the 270th day after the date hereof   ..................   100.00% of all Registrable Securities
</TABLE>

     (c) Notwithstanding Sections 9 (a) and (b), the Holder may Transfer the
Registrable Securities in a cumulative aggregate amount up to the limits as set
forth below:

<TABLE>
At any time following:
<S>                                                        <C>
the 120th day after the date hereof   ..................   48.72% of all Registrable Securities

the 150th day after the date hereof   ..................   58.97% of all Registrable Securities

the 180th day after the date hereof   ..................   69.23% of all Registrable Securities

the 210th day after the date hereof   ..................   79.49% of all Registrable Securities

the 240th day after the date hereof   ..................   89.74% of all Registrable Securities

the 270th day after the date hereof   ..................   100.00% of all Registrable Securities
</TABLE>

     (d) Notwithstanding Sections 9(a), (b) and (c), Holder may Transfer any or
all of the Registrable Securities at any time to any wholly-owned subsidiary of
the Holder (a "Holder Subsidiary"); provided, however, that (i) such Holder
               -----------------
Subisidiary agrees to be bound (as a Holder) to the provisions of this
Agreement, and (ii) for purposes of this Section 9, Holder and any Holder
Subsidiary shall be treated as a single entity such that Registrable Securities
held by Holder and any Holder Subisidiary shall be aggregated for the purposes
of calculating the cumulative aggregate limits on Transfer of Registrable
Securities in Sections 9(b) and (c) hereof.

     10. Miscellaneous.
         -------------

     (a) Notices. Unless otherwise provided herein, all notices, requests,
         -------
claims, demands and other communications hereunder shall be in writing and shall
be given (and shall be deemed to have been duly given upon receipt) by delivery
in Person, by facsimile transmission (with such facsimile transmission confirmed
by sending a copy of such notice, request, claim, demand or other communication
by certified mail, postage prepaid, return receipt requested), or mailed by
certified mail (postage prepaid, return receipt requested) or by a nationally
recognized courier service as follows:

if to the Company, to:

NetRatings, Inc.
890 Hillview Court
Milpitas, California  95035
Attention: Jason Gray, Esq.
Facsimile: (408) 957-0487

                                       10

<PAGE>

with a copy to:

Gray Cary Ware & Freidenrich LLP
400 Hamilton Avenue
Palo Alto, California 94301
Attention: Jon C. Perry, Esq.
Facsimile: (650) 833-2001

if to the Holder, to:

DoubleClick Inc.
450 West 33rd Street
New York, New York 10001
Attention: Jonathan Shapiro
Facsimile: (212) 287-7765

with a copy to:

Brobeck, Phleger & Harrison LLP
1633 Broadway, 47th Floor
New York, New York 10019
Attention: Scott L. Kaufman, Esq.
Facsimile: (212) 586-7878

or to such other place and with such other copies as either party may designate
as to itself by written notice to the other party in accordance with this
Section 10(a).

     (b) Amendments; No Waivers. The provisions of this Agreement may only be
         ----------------------
amended or waived pursuant to a writing executed by both the Company and the
Holder. No failure or delay by any party in exercising any right, power or
privilege hereunder shall operate as a waiver thereof, nor shall any single or
partial exercise thereof preclude any other or further exercise thereof or the
exercise of any other right, power or privilege. The rights and remedies herein
provided shall be cumulative and not exclusive of any rights or remedies
provided by law.

     (d) Successors and Assigns. Except as otherwise provided in this Agreement,
         ----------------------
no party hereto shall assign this Agreement or any rights or obligations
hereunder without the prior written consent of the other party hereto and any
such attempted assignment without such prior written consent shall be void and
of no force and effect; provided however, that (i) if the Registration Statement
is not effective prior to the Effectiveness Deadline, the Holder may assign its
rights hereunder without the consent of the Company to any transferee of
Registrable Securities that (A) is a transferee of at least 7.69% of the
Registrable Securities and (B) agrees to be bound (as a Holder) to the
provisions of this Agreement. The provisions of this Agreement shall be binding
upon and inure to the benefit of the parties hereto and their respective
successors and permitted assigns.

     (e) Governing Law; Forum. THIS AGREEMENT SHALL BE GOVERNED BY, AND
         --------------------
CONSTRUED AND ENFORCED IN ACCORDANCE WITH, THE LAWS OF THE STATE OF CALIFORNIA
OTHER THAN CONFLICT OF LAWS PRINCIPLES THEREOF

                                       11

<PAGE>

DIRECTING THE APPLICATION OF ANY LAW OTHER THAN THAT OF THE STATE OF CALIFORNIA.

     (f) Waiver of Jury Trial. TO THE FULLEST EXTENT PERMITTED BY LAW, EACH
         --------------------
PARTY HERETO HEREBY IRREVOCABLY WAIVES ALL RIGHT TO TRIAL BY JURY IN ANY
PROCEEDING (WHETHER BASED ON CONTRACT, TORT OR OTHERWISE) ARISING OUT OF OR
RELATING TO THIS AGREEMENT OR ANY TRANSACTION OR AGREEMENT CONTEMPLATED HEREBY
OR THE ACTIONS OF ANY PARTY HERETO IN THE NEGOTIATION, ADMINISTRATION,
PERFORMANCE OR ENFORCEMENT HEREOF.

     (g) Counterparts; Effectiveness. This Agreement may be signed in any number
         ---------------------------
of counterparts (including by facsimile), each of which shall be an original,
with the same effect as if the signatures thereto and hereto were upon the same
instrument. This Agreement shall become effective when each party hereto shall
have received a counterpart hereof signed by the other party hereto.

     (h) No Third Party Beneficiaries; Severability. This Agreement is not
         ------------------------------------------
intended to confer upon any Person other than the parties hereto any rights or
remedies hereunder. If any term or other provision of this Agreement is invalid,
illegal or incapable of being enforced by any rule of law or public policy, all
other terms and provisions of this Agreement shall nevertheless remain in full
force and effect.

     (i) Headings; Interpretation. The descriptive headings contained in this
         ------------------------
Agreement are included for convenience of reference only and shall not affect in
any way the meaning or interpretation of this Agreement. The parties have
participated jointly in the negotiation and drafting of this Agreement. In the
event an ambiguity or question of intent or interpretation arises, this
Agreement shall be construed as if drafted jointly by the parties, and no
presumption or burden of proof shall arise favoring or disfavoring any party by
virtue of the authorship of any provisions of this Agreement.

                  [Remainder of Page Intentionally Left Blank]

                                       12

<PAGE>

     IN WITNESS WHEREOF, the parties hereto have caused this Agreement to be
duly executed by their respective authorized officers as of the day and year
first above written.

                                                  NETRATINGS, INC.

                                                  By:    /s/  Todd Sloan
                                                  Name:  Todd Sloan
                                                  Title: Chief Financial Officer

                                                  DOUBLECLICK INC.

                                                  By:    /s/  Jonathan Shapiro
                                                  Name:  Jonathan Shapiro
                                                  Title: Chief Strategy Officer<PAGE>
                                                                     Exhibit 4.3

             SECOND ADDENDUM to the SECOND RESTATED RIGHTS AGREEMENT

This Second Addendum ("Second Addendum") to the Second Restated Rights Agreement
                       ---------------
dated September 22, 1999 executed by and between NetRatings, Inc., a Delaware
corporation (the "Company"), and the Investors, as defined within said agreement
                  -------
(the "Agreement"), as amended in the First Addendum to the Second Restated
      ---------
Rights Agreement dated as of September 22, 1999 (the "First Addendum"), is made
                                                      --------------
effective as of May 6, 2002 (the "Amendment Effective Date").
                                  ------------------------

Whereas the Company is entering in that certain Asset Purchase Agreement
effective as of the Amendment Effective Date (the "Asset Purchase Agreement"),
                                                   ------------------------
whereby the Company shall purchase certain of the assets of DoubleClick Inc., a
Delaware corporation ("DoubleClick");
                       -----------

Whereas as a condition of the Asset Purchase Agreement, DoubleClick is to be
granted certain rights requiring the Company to register shares of the Company's
Common Stock issued to DoubleClick on a registration statement to be filed with
the United States Securities and Exchange Commission under a registration rights
agreement by and between the Company and DoubleClick effective as the Amendment
Effective Date and in substantially the form as attached hereto as Exhibit A
                                                                   ---------
(the "Registration Rights Agreement");
      -----------------------------

Whereas Nielsen Media Research, Inc., a Delaware corporation, and ACNielsen,
Inc., a Delaware corporation, collectively are holders of a majority of the
outstanding shares of Registrable Securities;

Whereas, Section 3.7 of the Agreement permits any provision of the Agreement to
be amended with the written consent of the holders of at least a majority of the
outstanding shares of Registrable Securities; and

Whereas the parties desire to amend Section 1.8 of the Agreement.

     NOW, THEREFORE, in consideration of the mutual understandings and promises
set forth above and below in this Second Addendum, the Company and the Investors
hereby amend the Agreement, as amended by the First Addendum thereto, as
follows:

     1. Defined Terms. Each term used but not defined in this Second Addendum
        -------------
shall have the meaning given in the Agreement.

     2. Amendment. Section 1.8 of the Agreement is hereby amended and restated
        ---------
in its entirety as follows:

     "1.8 Limitations on Subsequent Registration Rights.

          (a) From and after the date of this Agreement, the Company shall not
enter into any agreement granting any holder or prospective holder of any
securities of the Company registration rights with respect to such securities
without the prior written consent of a majority of the Registrable Securities
then outstanding (on a Common Stock equivalent basis) unless (1) such new
registration rights, including standoff obligations, are on a PARI PASSU basis
with those rights of the Holders hereunder, or (2) such new registration rights,
including standoff obligations, are subordinate to the registration rights
granted the Holders hereunder, provided that the inclusion of such holder's
securities shall not reduce the amount of Registrable Securities which are
included in any registration for which the Holders hold registration rights
pursuant to this Agreement.

<PAGE>

          (b) Notwithstanding the foregoing, the Company is hereby authorized to
enter into that certain Registration Rights Agreement dated May 6, 2002 (the
"DoubleClick Registration Rights Agreement"), by and between the Company and
 -----------------------------------------
DoubleClick Inc., a Delaware corporation ("DoubleClick"), and, provided further,
                                           -----------
that without the written consent of DoubleClick (on the one hand) and the
holders of a majority of the outstanding shares of Registrable Securities (on
the other hand), no Registrable Securities shall be eligible for registration
under any registration statement filed by the Company in fulfillment of its
obligations under such DoubleClick Registration Rights Agreement.

     3. Full Force. Except as expressly set forth above, the Agreement shall
        ----------
remain in full force and effect as written.

This Second Addendum of the Agreement has been executed in duplicate by the
authorized representatives of the parties.

NETRATINGS, INC.                                NIELSEN MEDIA RESEARCH, INC.

By:  /s/  William Pulver                        By:  /s/  David H. Harkness

Name:  William Pulver                           Name:  David H. Harkness

Title:  President and Chief Executive Officer   Title:  Senior Vice President

ACNIELSEN, INC.

By:  /s/  Earl H. Doppelt

Name:  Earl H. Doppelt

Title:  Executive Vice President and General Counsel

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