<PAGE>

                                                                   Exhibit 10.28

NO TRANSFER, SALE, ASSIGNMENT, PLEDGE, HYPOTHECATION OR OTHER DISPOSITION OF
THIS NOTE MAY BE MADE EXCEPT (A) PURSUANT TO A REGISTRATION STATEMENT
EFFECTIVE UNDER THE SECURITIES ACT OF 1933, AS AMENDED, OR (B) IF MAKER HAS
BEEN FURNISHED WITH AN OPINION REASONABLY SATISFACTORY IN FORM AND SUBSTANCE
TO MAKER OF COUNSEL REASONABLY SATISFACTORY TO MAKER THAT SUCH TRANSFER,
SALE, ASSIGNMENT, PLEDGE, HYPOTHECATION OR OTHER DISPOSITION IS EXEMPT FROM
THE PROVISIONS OF SECTION 5 OF THE SECURITIES ACT OF 1933, AS AMENDED, AND
THE RULES AND REGULATIONS THEREUNDER.


     ISSUE PRICE: $759.918 PER $1,000 OF PRINCIPAL AMOUNT
     TOTAL ISSUE PRICE:  $340,000,000
     ORIGINAL ISSUE DISCOUNT: $240.082 PER $1,000 OF PRINCIPAL AMOUNT
     TOTAL AMOUNT OF ORIGINAL ISSUE DISCOUNT:  $107,416,805
     YIELD TO MATURITY: 4.0% per annum
     ISSUE DATE:  November 30, 1999

                              SUBORDINATED ZERO COUPON
                           CONVERTIBLE DEBENTURE due 2006
                                representing up to
                                    $447,416,805

No. 2.                                                       November 30, 1999

          1.   PAYMENT OF PRINCIPAL AND ORIGINAL ISSUE DISCOUNT.

          FOR VALUE RECEIVED, the undersigned, NBC Internet, Inc., a Delaware
corporation ("Maker"), hereby promises to pay GE Investments Subsidiary, Inc.
(or an affiliate thereof) or the subsequent registered owner of this Note
("Payee"), in the manner hereinafter provided, the principal amount of Four
Hundred Forty Seven Million Four Hundred Sixteen Thousand Eight Hundred Five
Dollars ($447,416,805) on November 30, 2006 (the "Stated Maturity Date").

          The principal of this Note shall not bear interest except in the
case of a default in the payment of principal upon acceleration, upon
redemption or at the Stated Maturity Date and in such case the amount payable
hereon, in lieu of the principal amount due at the Stated Maturity Date
hereof shall be the amount (the "Amortized Face Amount") equal to (a) the
Issue Price (as defined below) plus (b) that portion of the difference
between the Issue Price and the principal amount that has accrued at the
Yield to Maturity (as defined below) (calculated on an annual bond equivalent
basis from November 30, 1999) at the date as of which the Amortized Face
Amount is calculated, which shall accrue from the date of such default in
payment to the date payment on such principal has been made or duly provided
for. Interest on any overdue principal shall be payable on demand. Any such
interest on any overdue principal that is not so paid on demand shall bear
interest at the Yield to Maturity, which shall accrue from the date of such
demand for payment to the date payment of such interest has been made or duly
provided for, and such interest shall also be payable on demand.  As used
herein, the term "Issue Price" means the principal amount of this Note less
the Original Issue Discount stated on the face


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                                                                            2


hereof, and the term "Yield to Maturity" means the Yield to Maturity stated
on the face hereof for the period from the Original Issue Date stated on the
face hereof to the Stated Maturity Date.

          This Note is issued pursuant to the Second Amended and Restated
Agreement and Plan of Contribution, Investment and Merger, dated as of July
8, 1999, as amended (the "Merger Agreement"), among National Broadcasting
Company, Inc., Payee, Neon Media Corporation, Maker and Xoom.com, Inc.
Subject to the right of Payee to convert this Note pursuant to Section 2,
this Note may be redeemed in whole at any time after November 30, 2004 at the
option of Maker without penalty or premium, at a redemption price equal to
the Amortized Face Amount, upon at least thirty (30) days prior written
notice thereof to Payee. Maker may pay the redemption price in cash, Common
Stock (as defined below) or both, PROVIDED that in any event the issuance of
6,533,352 shares of Common Stock shall be deemed to be full satisfaction of
the redemption price. Any Common Stock issued to pay the redemption price
shall be valued based on the average closing price for the 30-day period
ending the day prior to the date of redemption. All payments to be made
hereunder shall be made to Payee at 30 Rockefeller Plaza, New York, New York
10012 (Attention:  Chief Financial Officer).

          2. CONVERSION RIGHT.

          (a) CONVERSION.  Payee has the right, at its option, at any time after
     November 30, 2000, to convert all (but not less than all) of the principal
     of this Note into an aggregate of 5,338,357 fully paid and nonassessable
     shares (as adjusted pursuant to Section 2(b), the "Conversion Shares") of
     Class B common stock, par value $.0001 per share, of Maker ("Common Stock")
     upon surrender of this Note at the office of Maker.  Upon the receipt of
     this Note, duly endorsed, and a signed notice from Payee that Payee is
     irrevocably exercising its conversion right pursuant to this Section 2(a),
     Maker shall promptly deliver the Conversion Shares registered in the name
     of Payee.

          (b) ADJUSTMENTS.  The conversion rights set forth are subject to
     adjustment as provided below.

          (i)    STOCK SPLITS, STOCK DIVIDENDS AND COMBINATIONS.  If Maker shall
          at any time subdivide the outstanding shares of Common Stock or shall
          issue a stock dividend with respect to the Common Stock, then the
          number of shares of Common Stock for which this Note is convertible
          immediately prior to that subdivision shall be proportionately
          increased, and if Maker shall at any time combine the outstanding
          shares of Common Stock, then the number of shares of Common Stock for
          which this Note is exercisable immediately prior to that combination
          shall be proportionately reduced.  Any adjustment under this Section
          2(b)(i) shall become effective at the close of business on the date
          the subdivision, stock dividend or combination becomes effective.

          (ii)   RECLASSIFICATION, EXCHANGE, SUBSTITUTION AND IN-KIND
          DISTRIBUTION.  If the Common Stock issuable on conversion of this Note
          shall be changed into the


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                                                                             3


          same or a different number of shares of any other class or classes
          of stock, whether by capital reorganization, reclassification, or
          otherwise (other than a subdivision or combination of shares provided
          for above) or upon the payment of a dividend in cash, securities or
          property other than Common Stock, then Payee shall, upon conversion
          of this Note, be entitled to receive, in lieu of the Common Stock
          that Payee would have become entitled to receive but for such change,
          that number of shares of such other class or classes of stock that is
          equivalent to the number of shares of Common Stock that Payee would
          have received had Payee converted this Note immediately prior to that
          change.  Following any reclassification, exchange, substitution or
          in-kind distribution, Maker shall promptly issue to Payee a new Note
          for such new securities or other property.  The new Note shall
          provide for adjustments which shall be nearly equivalent as may be
          reasonably practicable to the adjustments provided for in this
          Section 2(b) including, without limitation, adjustments to the number
          of securities or property issuable upon conversion of the new Note.
          The provisions of this Section 2(b)(ii) shall similarly apply to
          successive reclassifications, exchanges, substitutions or other
          events and successive dividends.

          (iii)  REORGANIZATIONS, MERGERS, CONSOLIDATIONS OR SALE OF ASSETS.  In
          case of any merger of Maker with or into another company (other than a
          merger with another company in which Maker is a continuing company and
          which does not result in any reclassification or change of outstanding
          securities issuable upon conversion of this Note), consolidation or in
          case of any sale of all or substantially all of the assets of Maker,
          Maker shall, as condition precedent to such transaction, execute a new
          Note or cause such successor or purchasing company, as the case may
          be, to execute a new Note, providing that Payee shall have the right
          to convert such new Note and upon such conversion to receive, in lieu
          of each share of Common Stock theretofore issuable upon conversion of
          this Note, the kind and amount of shares of stock, other securities,
          money and property issuable or payable, as the case may be, upon such
          merger, consolidation, sale of assets or other change to a holder of
          one share of Common Stock.  Such new Note shall provide for
          adjustments that shall be as nearly equivalent as may be reasonably
          practicable to the adjustments provided for in this Section 2(b).  The
          provisions of this Section 2(b)(iii) shall similarly apply to
          successive mergers, consolidations, sale of assets and other changes
          and transfers.

          (iv)   NOTICE OF ADJUSTMENTS.  Maker shall promptly give written
          notice of each adjustment or readjustment of the number of shares of
          Common Stock or other securities issuable upon conversion of this
          Note, by first class mail, postage prepaid, to the Payee at the
          Payee's address for notices in the Merger Agreement.  This notice
          shall state that adjustment or readjustment and show in reasonable
          detail the facts on which the adjustment or readjustment is based.
          Maker further agrees to notify Payee in writing of a reorganization,
          merger or sale in accordance with Section 2(b)(iii) at least thirty
          (30) days prior to the effective date thereof.


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                                                                             4


          (v)    NO CHANGE NECESSARY.  The form of this Note need not be changed
          because of any adjustment in the number of shares of Common Stock
          issuable upon its conversion.  A Note issued after any adjustment on
          conversion or upon replacement may continue to express the same number
          of shares of Common Stock as are stated on this Note as initially
          issued, and such number of shares shall be considered to have been so
          changed as of the close of business on the date of adjustment.

          (vi)   RESERVATION OF STOCK.  Maker covenants that it will at all
          times reserve and keep available, for issuance upon conversion of this
          Note, such shares of its Common Stock from time to time issuable upon
          conversion of this Note, and if at any time the number of authorized
          but unissued shares of Common Stock shall not be sufficient to effect
          the conversion of this Note, Maker will take such corporate action as
          may, in the opinion of its counsel, be reasonably necessary to
          increase its authorized but unissued shares of Common Stock to such
          number of shares as shall be sufficient for such purpose.  Issuance of
          this Note shall constitute full authority to Maker's officers who are
          charged with the duty of executing stock certificates to execute and
          issue the necessary certificates for shares of Common Stock issuable
          upon the conversion of this Note.

          (vii)  NOTICES OF RECORD DATE.  In the event Maker intends to declare
          a record date for the holders of Common Stock for the purpose of
          determining the holders thereof who are entitled to receive any
          dividend or other distribution, Maker shall mail to Payee of this Note
          at least ten days prior to the proposed record date specified therein,
          a notice specifying the date on which any such record is to be taken
          for the purpose of such dividend or distribution.

          (viii) NO IMPAIRMENT.  Maker shall not, by amendment of its
          Certificate of Incorporation or through a reorganization, transfer of
          assets, consolidation, merger, dissolution, issue or sale of
          securities or any other voluntary action, avoid or seek to avoid the
          observance or performance of any of the terms to be observed or
          performed under this Note by Maker, but shall at all time in good
          faith assist in carrying out of all the provisions of this Section
          2(b) and in taking all such action as may be reasonably necessary or
          appropriate to protect Payee's rights under this Section 2(b) against
          impairment.

          (c) GOVERNANCE RIGHTS.  Upon conversion of this Note pursuant to
     Section 2(a), and conversion of the Zero Coupon Convertible Debenture due
     2006 representing up to $39,477,953 issued by Maker to NBC Multimedia,
     Inc., Payee shall have the right to elect one additional director to the
     Board of Directors of Maker pursuant to the Certificate of Incorporation of
     Maker.


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                                                                             5


          3.  REPRESENTATIONS AND WARRANTIES OF MAKER.  Maker hereby
represents and warrants to Payee that: (a) Maker is duly organized, validly
existing and in good standing under the laws of its jurisdiction of
organization, has the full power and authority, and the legal right, to make,
deliver and perform this Note and its obligations hereunder on the terms and
conditions hereof and has taken all necessary corporate action to authorize
the execution, delivery and performance of this Note and to authorize the
borrowing hereunder, and this Note has been duly executed and delivered on
behalf of Maker; (b) this Note constitutes a legal, valid and binding
obligation of Maker enforceable against it in accordance with its terms,
except as enforceability may be limited by applicable bankruptcy, insolvency,
reorganization, moratorium or similar laws affecting the enforcement of
creditors' rights generally and by general equitable principles (whether
enforcement is sought by proceedings in equity or at law); (c) the execution,
delivery and performance of this Note, the borrowing hereunder and the use of
the proceeds thereof will not violate any material requirement of law, any
material contractual obligation of Maker or its subsidiaries or any of their
applicable charters, bylaws or similar documents; and (d) no Event of Default
(as defined below) has occurred and is continuing.

          4.  REPRESENTATIONS AND WARRANTIES OF PAYEE.  Payee hereby
represents and warrants to Maker that: (a) Payee is duly organized, validly
existing and in good standing under the laws of its jurisdiction of
organization, has the full power and authority, and the legal right, to make
the loan to Maker evidenced by this Note and has taken all necessary
corporate action to authorize the making of such loan, and this Note has been
duly executed and delivered on behalf of Payee; (b) Payee is an "accredited
investor" within the meaning of Regulation D of the Securities Act of 1933,
as amended (the "Securities Act") and is being issued this Note for its own
account and not with a view to the distribution thereof in violation of the
Securities Act; (c) Payee understands and acknowledges that this Note has not
been registered under the Securities Act and may be offered and resold only
if registered pursuant to the provisions of the Securities Act or if an
exemption from registration is available, except under circumstances where
neither such registration nor such exemption is required by law, and that
Maker is not required to register this Note; and (d) Payee has had access to
such financial and other information concerning Maker as it deemed necessary
in connection with the issuance of this Note.

          5. EVENTS OF DEFAULT.  An Event of Default occurs if:  (1) Maker
pursuant to or within the meaning of Title 11 of the U.S. Code or any similar
federal or state law for the relief of debtors (a "Bankruptcy Law"):  (a)
commences a voluntary case, (b) consents to the entry of an order for relief
against it in an involuntary case, (c) consents to the appointment of a
receiver, trustee, assignee, liquidator, custodian or similar official under
any Bankruptcy Law (a "Custodian") or (d) makes a general assignment for the
benefit of its creditors; or (2) a court of competent jurisdiction enters an
order or decree under any Bankruptcy Law that:  (a) is for relief against
Maker as debtor in an involuntary case, (b) appoints a Custodian of Maker, or
(c) orders the liquidation of Maker, and the order or decree remains unstayed
and in effect for 90 days; or (3) a Change of Control (as defined below)
occurs, or (4) Maker fails to pay the principal amount due at the Stated
Maturity Date.  Upon the occurrence of an Event of Default, Payee shall have
the option to receive either (i) the number of Conversion Shares Payee would
have received if Payee had exercised its rights under Section 2 immediately
prior to such Event of Default or (ii)


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                                                                             6


either (A) in the event of a default pursuant to (1), (2) or (3) above, the
Amortized Face Amount or (B) in the event of a default pursuant to (4) above,
the principal amount due at the Stated Maturity Date plus accrued interest
thereon from the Stated Maturity Date at the Yield to Maturity.  In the case
of either (i) or (ii), the obligations of Payee shall immediately become due
and payable.  As used herein the term "Change of Control" means any of the
following: (i) a merger, consolidation or other business combination or
transaction to which a Maker is a party if the shareholders of Maker
immediately prior to the effective date of such merger, consolidation or
other business combination or transaction, do not have beneficial ownership
of voting securities representing 50% or more of the total voting power of
the surviving corporation or its parent immediately following such merger,
consolidation or other business combination or transaction; (ii) any person
or entity shall have beneficial ownership of 20% or more of the outstanding
shares of Class A Stock (as such term is defined in Maker's Certificate of
Incorporation) at a time when the holders of Common Stock do not elect a
majority of the Board of Directors of Maker; (iii) a sale of all or
substantially all of the consolidated assets of Maker to another person or
entity or (iv) a liquidation or dissolution of Maker.


          6. SUBORDINATION.  Payee agrees that payment of the principal of and
interest on this Note shall be subordinated in right of payment to the prior
payment in full of all Senior Debt at any time outstanding.  Notwithstanding the
immediately preceding sentence, such subordination shall not limit the payment
of principal of and interest on this Note in accordance with its terms unless,
at the time of such payment, there is a default in the payment of principal of
or interest on such Senior Debt, there exists any event which, with the giving
of notice or the passage of time, is reasonably likely to give rise to a default
under such Senior Debt, or in the event that a default under this Note has
caused a default under such Senior Debt.  The limitation on payments under this
Note shall continue until such time as the default on such Senior Debt has been
cured or waived.  The provisions of this paragraph are intended solely for the
purpose of defining the relative rights of the Payee of this Note, on the one
hand, and the holder of Senior Debt, on the other hand.  "Senior Debt" shall
mean (a) any and all liabilities of Maker recorded on the Maker's balance sheet
or in the footnotes thereto in accordance with GAAP (as defined below); (b) the
principal of, premium (if any), interest on, and other moneys due which arise
out of any indebtedness of Maker (or any refinancing thereof): (1) for borrowed
funds; (2) due to sellers or lessors of any real or personal property to Maker;
or (3) for reimbursement obligations with respect to letters of credit, except
in each case referred to in subclauses (1), (2) and (3) above, to the extent the
holder of such indebtedness otherwise agrees in writing; (c) any other
indebtedness of Maker, except to the extent that the holder of such indebtedness
otherwise agrees in writing; and (d) any debentures, notes or other evidence of
indebtedness issued in exchange for any of the foregoing indebtedness, or any
indebtedness arising from the satisfaction of such indebtedness by a guarantor.
"GAAP" means generally accepted accounting principles set forth from time to
time in the opinions and pronouncements of the Accounting Principles Board and
the American Institute of Certified Public Accountants and statements and
pronouncements of the Financial Accounting Standards Board (or agencies with
similar functions of comparable stature and authority within the U.S. accounting
profession).  The provisions of this Section 6 shall not apply to conversions
pursuant to Section 2.


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                                                                             7


          7. BUSINESS DAY.  If any payment or conversion shall be required by
the terms hereof to be made on a day that is not a Business Day (as defined
below), such payment or conversion shall be made on the immediately succeeding
Business Day.  For purposes hereof, "Business Day" shall mean a day other than a
Saturday, Sunday, holiday or other day on which commercial banks in the State of
New York are authorized or required by law to close.

          8.NO WAIVER.  No action or omission by Payee shall constitute a waiver
of any rights or remedies of Payee hereunder.  Such rights and remedies are
cumulative and not exclusive of any rights or remedies provided by law.

          9. AMENDMENT; ASSIGNMENT . The terms of this Note may be amended,
supplemented or modified only with the written consent of Maker and Payee.  This
Note shall be binding upon and inure to the benefit of Maker, Payee and their
respective successors and assigns, except that neither Payee nor Maker may
assign or transfer any of its rights or obligations under this Note without the
prior written consent of the other party.  In the event of any assignment or
transfer by Payee with the prior written consent of Maker, Maker shall, upon the
request of the transferee and receipt of this Note from transferee, reissue this
Note in the name of the transferee.

          10.  GOVERNING LAW; JURISDICTION.  This Note is made and delivered in
New York, New York, and, pursuant to Section 5-1401 of the General Obligations
Law of the State of New York, shall be governed by and construed and interpreted
in accordance with the laws of the State of New York applicable to contracts
fully performed in New York.  All judicial actions, suits or proceedings brought
against Maker or Payee with respect to its obligations, liabilities or any other
matter under or arising out of or in connection with this Note or for
recognition or enforcement of any judgment rendered in any such proceedings
shall be brought exclusively in any state or federal court located in the County
of New York.

          11.  MUTILATED, DESTROYED OR MISSING NOTES.  If this Note is mutilated
and surrendered to Maker or Maker receives evidence to its satisfaction of the
destruction, loss or theft of this Note, Maker shall issue a replacement Note.
If required by Maker, an indemnity bond must be supplied by Payee that is
sufficient in the judgment of Maker to protect Maker from any loss it may suffer
if this Note is replaced.  Maker may charge for any expenses of replacing this
Note.

          IN WITNESS WHEREOF, Maker has caused this Note to be duly issued as of
the date first above written.

                                        NBC INTERNET, INC.


                                        By:  /s/ John Harbottle
                                           -----------------------------------
                                           Name:   John Harbottle
                                           Title:  EVP Finance & CFO


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                                                                             8


ACKNOWLEDGED AND AGREED:


GE INVESTMENTS SUBSIDIARY, INC.


By:  /s/ Robert E. Healing
   -----------------------------------------
   Name:   Robert E. Healing
   Title:  Vice President