<PAGE>

                                                            Exhibit 10.27

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:  $30,000,000
       ORIGINAL ISSUE DISCOUNT: $240.082 PER $1,000 OF PRINCIPAL AMOUNT
       TOTAL AMOUNT OF ORIGINAL ISSUE DISCOUNT:  $9,477,953
       YIELD TO MATURITY: 4.0% per annum
       ISSUE DATE:  November 30, 1999

                              SUBORDINATED ZERO COUPON
                           CONVERTIBLE DEBENTURE due 2006
                                representing up to
                                    $39,477,953

No. 1.                                                        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 NBC Multimedia,
       Inc. (or an affiliate thereof) or the subsequent registered owner of this
       Note ("Payee"), in the manner hereinafter provided, the principal amount
       of Thirty Nine Million Four Hundred Seventy Seven Thousand Nine Hundred
       Fifty-Three Dollars ($39,477,953) 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"

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                                                                            2


       means the principal amount of this Note less the Original Issue
       Discount stated on the face 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 568,118 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 471,031 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.


<PAGE>

                                                                            3

              (ii)   RECLASSIFICATION, EXCHANGE, SUBSTITUTION AND IN-KIND
              DISTRIBUTION.  If the Common Stock issuable on conversion of this
              Note shall be changed into the 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 the adjustment or readjustment and show in
              reasonable


<PAGE>

                                                                            4

              detail the facts on which that 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.

              (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 $447,416,805 issued by Maker to GE Investments
       Subsidiary, Inc., Payee shall have the


<PAGE>

                                                                            5

       right to elect one additional director to the Board of Directors of
       Maker pursuant to the Certificate of Incorporation of Maker.

              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


<PAGE>

                                                                            6

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) 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



<PAGE>

                                                                            7

stature and authority within the U.S. accounting profession).  The provisions
of this Section 6 shall not apply to conversions pursuant to Section 2.

              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





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                                                                            8



              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



ACKNOWLEDGED AND AGREED:


NBC MULTIMEDIA, INC.


By: /s/ Martin J. Yudkovitch
    -------------------------------
    Name:  Martin J. Yudkovitch
    Title: President