<PAGE>

                                                                    EXHIBIT 10.5
                                                                    ------------


          THIS SECURITY IS NOT BEING REGISTERED UNDER THE SECURITIES ACT OF
1933, AS AMENDED (THE "SECURITIES ACT"). THE HOLDER HEREOF, BY PURCHASING THIS
SECURITY, AGREES FOR THE BENEFIT OF THE COMPANY THAT THIS SECURITY MAY BE
RESOLD, PLEDGED OR OTHERWISE TRANSFERRED, ONLY (1) TO THE COMPANY, OR (2)
PURSUANT TO AN EXEMPTION FROM REGISTRATION UNDER THE SECURITIES ACT.

          THE HOLDER OF THIS NOTE IS ENTITLED TO THE BENEFITS OF THE GUARANTEE
AND SECURITY AGREEMENT DATED NOVEMBER 8, 2001 AMONG THE COMPANY, CERTAIN
SUBSIDIARY GUARANTORS THERETO AND COMPAQ FINANCIAL SERVICES CORPORATION, AS
AMENDED, MODIFIED AND SUPPLEMENTED FROM TIME TO TIME. ADDITIONALLY, THE HOLDER
OF THIS NOTE IS ENTITLED TO THE BENEFITS OF THE AMENDMENT TO AND RESTATEMENT OF
THE INVESTOR RIGHTS AGREEMENT DATED NOVEMBER 8, 2001 AMONG THE COMPANY, COMPAQ
FINANCIAL SERVICES CORPORATION AND CMGI, INC., AS AMENDED, MODIFIED AND
SUPPLEMENTED FROM TIME TO TIME.


                                 NAVISITE, INC.

                      12% Convertible, Senior, Secured Note
                              Due December 31, 2007

U.S. $10,000,000                                                November 8, 2001


          FOR VALUE RECEIVED, the undersigned, NaviSite, Inc., a Delaware
corporation (the "Company"), hereby promises to pay to CMGI, Inc., a Delaware
corporation (the "Purchaser"), the principal sum of US$10,000,000 in twelve
equal quarterly installments (each a "Principal Payment"), together with accrued
but unpaid interest thereon, commencing on the first Interest Payment Date (as
defined below) in 2005 and continuing on each Interest Payment Date thereafter
(each date on which a Principal Payment is made, a "Principal Payment Date")
until December 31, 2007 (the "Maturity Date"). The Company may not prepay this
Note. Interest on the outstanding principal shall be at a rate of 12% per annum
("Interest"), calculated on the basis of a 360 day year consisting of twelve 30
day months, and will be payable quarterly in arrears on March 31, June 30,
September 30 and December 31 of each year (each an "Interest Payment Date")
beginning December 31, 2001 until the Maturity Date. Interest for the first
Interest Payment Date shall be calculated from the date of issuance hereof to
the first Interest Payment Date. If all or a portion of a Principal Payment or
Interest shall not be paid when due (whether at its stated maturity, by
acceleration or otherwise), the Company hereby promises to pay, on demand,
interest on such overdue amount from and including the due date to, but
excluding, the date such
<PAGE>

amount is paid in full at 14% per annum (and until the date such overdue amount
is paid in full, "Interest" on such overdue amount shall mean interest at such
rate).

          This Note is being delivered pursuant to a Note Purchase Agreement,
dated as of October 29, 2001, among the Company, the Purchaser and Compaq
Financial Services Corporation, a Delaware corporation (the "Note Purchase
Agreement"). This Note is one of the Notes referred to in the Note Purchase
Agreement, which among other things, contains provisions for the acceleration of
the maturity hereof upon the happening of certain events and for the amendment
or waiver of certain provisions of the Note Purchase Agreement, all upon the
terms and conditions therein specified.

          1.   Certain Definitions. As used herein, the following terms have the
following meanings:

          "Closing Price" shall mean, on any day, (i) the closing price of the
Common Stock (or any other security for which a closing price must be
determined) on a national securities exchange or as quoted on the Nasdaq
National Market on such day, as reported by the Wall Street Journal or (ii) if
the Common Stock (or any such other security) is quoted on the Nasdaq National
Market but no sale occurs on such day, the average of the closing bid and asked
prices of the Common Stock (or any such other security) on the Nasdaq National
Market on such day, as reported by the Wall Street Journal or (iii) if the
Common Stock (or any such other security) is not so listed or quoted, the
average of the closing bid and asked prices of the Common Stock (or any such
other security) in the U.S. over-the-counter market or (iv) if no such trading
market is readily available, the fair market value of the Common Stock (or any
such other security) as determined in accordance with Section 5(b) hereof.

          "Current Market Price" of the Common Stock means the average of the
daily Closing Prices of the Common Stock for the five consecutive trading days
selected by the board of directors commencing not more than 20 trading days
before, and ending not later than the date immediately preceding the record date
fixed in connection with such event or, if there is no record date, the date of
such event; provided, that the Current Market Price of the Common Stock in
connection with a Spin-Off shall mean the average of the daily Closing Prices of
the Common Stock for the same five consecutive trading days used to determine
the Fair Market Value of the securities being distributed in such Spin-Off.

          "Fair Market Value" of the securities to be distributed to the holders
of the Common Stock in connection with a Spin-Off shall mean the average of the
daily Closing Prices of such securities for a five consecutive trading day
period selected by the board of directors during the period beginning on the
first day of trading of such securities after the effectiveness of such Spin-Off
and ending not later than 20 days after the effectiveness of the Spin-Off.

                                       2
<PAGE>

          All capitalized terms used but not otherwise defined herein shall have
the meaning ascribed to such terms in the Note Purchase Agreement.

          2.   Security.

          The Purchaser's right to payment pursuant to the terms of this Note
shall be secured to the extent and on the terms and conditions set forth in the
Security Agreement, and the terms and provisions of the Security Agreement are
incorporated herein by reference.

          3.   Payment.

          Principal Payments on each Principal Payment Date and Interest on each
Interest Payment Date shall be made by bank cashier's check payable to the
Purchaser at the Purchaser's principal address set forth in Section 10.04 of the
Note Purchase Agreement (or at such other place as the Purchaser hereof shall
notify the Company in writing) or, if the Purchaser so specifies, by written
notice to the Company given not less than two Business Days prior to the
Principal Payment Date or the Interest Payment Date, as the case may be, by bank
wire transfer, in immediately available funds, to the account so specified, in
lawful money of the United States of America; provided that, at the election of
the Company, so long as the Company is listed on the Nasdaq National Market, up
to 100% of the amount of Interest due on any Interest Payment Date through and
including the Interest Payment Date in December 2007 may be paid in shares of
Common Stock. The number of shares of Common Stock to be issued in payment of
the Interest due on such Interest Payment Date shall equal the amount of such
Interest to be paid in Common Stock divided by the average of the Closing Prices
per share of the Common Stock on the five consecutive trading days ending on the
trading day immediately preceding such Interest Payment Date. If any Principal
Payment Date or any Interest Payment Date occurs on a date that is not a
Business Day, then the Principal Sum or Interest then due shall be paid on the
next succeeding Business Day.

          4.   Conversion.

                 (a)   Conversion Rights.  Subject to and in accordance with the
          provisions of this Section 4, at any time on or prior to the Maturity
          Date, the Purchaser may elect, in its sole discretion, to effect the
          conversion (the "Conversion") of all or any portion of the outstanding
          principal and interest due on this Note into shares of Common Stock.
          The number of shares of Common Stock into which the outstanding
          principal and accrued but unpaid interest (or portion thereof) shall
          be converted pursuant to this Section 4(a) shall be determined by
          dividing the amount of outstanding principal and interest the
          Purchaser has elected to convert by $0.26. The Conversion Price is
          subject to adjustment as provided in Section 5 hereof.

                                       3
<PAGE>

                 (b)   Manner of Effecting the Conversion.  If the Purchaser
          elects to effect the Conversion pursuant to Section 4(a) hereof, the
          Purchaser shall deliver a duly executed written notice to the Company
          of such election (the "Conversion Notice"), and in such event the
          Conversion shall be deemed to have been effected at the close of
          business on the date such Conversion Notice is given. Upon any
          Conversion of this Note in accordance with the terms hereof, the
          rights of the Purchaser with respect to the outstanding principal and
          all interest pursuant to this Note shall cease and the Purchaser shall
          be deemed to have become the holder of record of the shares of Common
          Stock into which this Note shall have been converted, provided that,
          if the Purchaser elects to convert only a portion of the outstanding
          principal and interest pursuant to Section 4(a) hereof, then the
          Company will deliver a new note to the Purchaser, on the same terms
          and conditions as this Note, with respect to the portion of the
          outstanding principal and interest that is not converted (the "New
          Note"). Concurrently with the delivery of a Conversion Notice, the
          Purchaser shall surrender this Note to the Company. Promptly upon its
          receipt of a Conversion Notice, the Company shall (i) deliver to or
          upon the written order of the Purchaser, a certificate or certificates
          for the number of shares of Common Stock issuable upon such
          Conversion, (ii) make a cash payment in respect of any fraction of a
          share as provided in Section 4(c) hereof and (iii) if applicable,
          deliver a New Note as set forth in this Section 4(b).

                 (c)   Fractional Shares.  No fractional shares shall be issued
          upon any Conversion. Instead of any fractional share which would
          otherwise be issuable upon a Conversion, the Company shall pay a cash
          amount in respect of such fractional share in an amount based upon the
          Closing Price of the Common Stock on the trading day immediately
          preceding such Conversion.

                 (d)   Notwithstanding anything contained herein, this Note may
          not be converted until the Company has obtained the stockholder
          approvals required in accordance with Rule 4350(i) of the National
          Association of Securities Dealers Manual and Delaware corporate law.

          5.   Antidilution Provisions.

                 (a)   The Conversion Price shall be subject to adjustment from
          time to time as follows:

                         (i)    Stock Splits and Combinations. In case the
                 Company shall at any time or from time to time after the
                 Closing Date (A) subdivide or split the outstanding shares of
                 Common Stock, (B) combine or reclassify the outstanding shares
                 of Common Stock into a smaller number of shares or (C) issue by

                                       4
<PAGE>

                 reclassification of the shares of Common Stock any shares of
                 Capital Stock of the Company, then, and in each such case, the
                 Conversion Price in effect immediately prior to such event or
                 the record date therefor, whichever is earlier, shall be
                 adjusted so that the holder of this Note thereafter surrendered
                 for conversion shall be entitled to receive the number of
                 shares of Common Stock or other securities of the Company which
                 such holder would have owned or have been entitled to receive
                 after the occurrence of any of the events described above, had
                 such Note been surrendered for conversion immediately prior to
                 the occurrence of such event or the record date therefor,
                 whichever is earlier. An adjustment made pursuant to this
                 subparagraph (i) shall become effective at the close of
                 business on the day upon which such corporate action becomes
                 effective. Such adjustment shall be made successively whenever
                 any event listed above shall occur.

                         (ii)   Stock Dividends in Common Stock.  In case the
                 Company shall at any time or from time to time after the
                 Closing pay a dividend or make a distribution in shares of
                 Common Stock on any class of Capital Stock of the Company other
                 than dividends or distributions of shares of Common Stock or
                 other securities with respect to which adjustments are provided
                 in Section 5(a)(i) above, the Conversion Price shall be
                 adjusted so that the holder of this Note shall be entitled to
                 receive upon conversion thereof, the number of shares of Common
                 Stock determined by multiplying (A) the applicable Conversion
                 Price by (B) a fraction, the numerator of which shall be the
                 number of shares of Common Stock theretofore outstanding and
                 the denominator of which shall be the sum of such number of
                 shares and the total number of shares issued in such dividend
                 or distribution.

                         (iii)  Issuance of Rights or Warrants.  In case the
                 Company shall issue to all holders of Common Stock rights or
                 warrants entitling such holders to subscribe for or purchase
                 Common Stock at a price per share less than the Current Market
                 Price, the Conversion Price in effect immediately prior to the
                 close of business on the record date fixed for determination of
                 stockholders entitled to receive such rights or warrants shall
                 be reduced by multiplying such Conversion Price by a fraction,
                 the numerator of which is the

                                       5
<PAGE>

                 sum of the number of shares of Common Stock outstanding at the
                 close of business on such record date and the number of shares
                 of Common Stock that the aggregate offering price of the total
                 number of shares of Common Stock so offered for subscription or
                 purchase would purchase at such Current Market Price and the
                 denominator of which is the sum of the number of shares of
                 Common Stock outstanding at the close of business on such
                 record date and the number of additional shares of Common Stock
                 so offered for subscription or purchase. For purposes of this
                 subparagraph (iii), the issuance of rights or warrants to
                 subscribe for or purchase securities convertible into Common
                 Stock shall be deemed to be the issuance of rights or warrants
                 to purchase the Common Stock into which such securities are
                 convertible at an aggregate offering price equal to the sum of
                 the aggregate offering price of such securities and the minimum
                 aggregate amount (if any) payable upon conversion of such
                 securities into Common Stock. Such adjustment shall be made
                 successively whenever any such event shall occur.

                         (iv)   Distribution of Indebtedness, Securities or
                 Assets.  In case the Company shall distribute to all holders of
                 Common Stock (whether by dividend or in a merger, amalgamation
                 or consolidation or otherwise) evidences of indebtedness,
                 shares of Capital Stock of any class or series, other
                 securities, cash or assets (other than Common Stock, rights or
                 warrants referred to in subparagraph (iii) above and other than
                 as a result of a Fundamental Change (as defined below)), the
                 Conversion Price in effect immediately prior to the close of
                 business on the record date fixed for determination of
                 stockholders entitled to receive such distribution shall be
                 reduced by multiplying such Conversion Price by a fraction, the
                 numerator of which is the Current Market Price on such record
                 date less the fair market value (as determined in good faith by
                 the board of directors, except in the case of a Spin-Off (as
                 defined below)) of the portion of such evidences of
                 indebtedness, shares of capital stock, other securities, cash
                 and assets so distributed applicable to one share of Common
                 Stock, and the denominator of which is the Current Market
                 Price. Such adjustment shall be made successively whenever any
                 such event shall occur.

                         In respect of a dividend or other distribution of
                 shares of Capital Stock of any class or series, or similar
                 equity interests, of or relating to a subsidiary or other
                 business unit of the Company (a "Spin-Off"), the adjustment to
                 the Conversion Price under this subparagraph (iv) shall occur
                 20 trading days after the effective date of the Spin-Off.

                         (v)    Issuance of Common Stock.  In case the Company
                 shall issue or sell any shares of Common Stock at a price per
                 share less than the Current Market Price (other than any (i)
                 such transaction as to which an adjustment is otherwise
                 provided for in this Section 5, (ii) the issuance by the
                 Company of

                                       6
<PAGE>

                 Common Stock to pay interest pursuant to Section 3 hereof or in
                 satisfaction of Affiliate Obligations, (iii) the issuance by
                 the Company to directors, employees, consultants or advisors of
                 the Company of shares of Common Stock, or grant of options or
                 other rights to purchase or acquire Common Stock, at a price,
                 or exercise price, as the case may be, no lower than the fair
                 market value of the Common Stock (as reasonably determined by
                 the independent directors of the Company in good faith as of
                 the time of issuance or grant, as the case may be), so long as
                 the aggregate number of shares of Common Stock that are so
                 issued or with respect to which an option or other right is so
                 granted under this clause (iii) does not exceed 14,500,000
                 shares or (iv) the issuance by the Company of Common Stock
                 pursuant to the NaviSite Warrants in accordance with their
                 terms as of the date hereof), the Conversion Price in effect
                 immediately prior to the close of business on the date
                 immediately preceding such issuance or sale shall be reduced by
                 multiplying such Conversion Price by a fraction, the numerator
                 of which is the sum of the number of shares of Common Stock
                 outstanding at the close of business on the date immediately
                 preceding such issuance or sale (giving assumed effect to the
                 conversion of all convertible securities outstanding on the
                 date hereof) to and the number of shares of Common Stock that
                 the aggregate price paid for the total number of shares of
                 Common Stock so issued or sold on such date would purchase at
                 such Current Market Price and the denominator of which is the
                 sum of the number of shares of Common Stock outstanding at the
                 close of business on the date immediately preceding such
                 issuance or sale (giving assumed effect to the conversion of
                 all convertible securities outstanding on the date hereof) and
                 the number of additional shares of Common Stock so issued or
                 sold. For purposes of this subparagraph (v), the issuance of
                 rights, options or warrants to purchase Common Stock or
                 securities convertible or exchangeable for Common Stock shall
                 be deemed to be the issuance of the Common Stock into which
                 such securities are exercisable at an aggregate price equal to
                 the sum of the aggregate price paid for such securities and the
                 minimum aggregate amount (if any) payable upon exercise or
                 conversion of such options, rights, warrants or securities for
                 Common Stock, and the date of issuance and sale for purposes
                 hereof shall be the date upon which such options, rights or
                 warrants were issued or amended. Such adjustment shall be made
                 successively whenever any such event shall occur; provided that
                 no adjustment shall be made upon exercise of any option, right
                 or warrant. If an adjustment is made as the result of the
                 issuance of an option, right, warrant or convertible security
                 and such option, right, warrant or

                                       7
<PAGE>

                 security expires unexercised or unconverted, the Conversion
                 Price shall be readjusted to the price that would have been in
                 effect if no such adjustment had been made.

                         (vi)   Fundamental Changes.  In case any transaction or
                 event (including, without limitation, any merger,
                 consolidation, combination, recapitalization, sale of assets,
                 tender or exchange offer, reclassification, compulsory share
                 exchange or liquidation) shall occur in which all or
                 substantially all outstanding shares of Common Stock are
                 converted into or exchanged or acquired for or constitute the
                 right to receive stock, other securities, cash, property or
                 assets (each, a "Fundamental Change"), the holder of this Note
                 outstanding immediately prior to the occurrence of such
                 Fundamental Change shall have the right upon any subsequent
                 conversion to receive (but only out of legally available funds,
                 to the extent required by applicable law) the kind and amount
                 of stock, other securities, cash, property or assets that such
                 holder would have received if such share had been converted
                 immediately prior thereto.

                 (b)     (i) Subject to paragraph (b)(ii) below, each
          determination of the Closing Price pursuant to clause (iv) of the
          definition of "Closing Price" shall be made in good faith by the
          Company. Upon each determination of the fair market value of the
          Common Stock by the Company hereunder, the Company shall promptly give
          notice thereof to each Purchaser, setting forth in reasonable detail
          the calculation of such fair market value and the method and basis of
          determination thereof (the "Company Determination").

                         (ii)   If the Required Holders shall disagree with the
                 Company Determination and shall by notice to the Company given
                 within 10 days after the Company's notice of the Company
                 Determination (an "Appraisal Notice") elect to dispute the
                 Company Determination, such dispute shall be resolved as set
                 forth in paragraph (b)(iii) below; provided that such procedure
                 shall not apply to any determination of fair market value made
                 pursuant to Section 5(a)(v)(ii).

                         (iii)  The Company shall within 10 days after an
                 Appraisal Notice shall have been given pursuant to paragraph
                 (b)(i) above engage an investment bank or other qualified
                 appraisal firm reasonably acceptable to the Required Holders
                 (the "Appraiser") to make an independent determination of the
                 fair market value of the Common Stock (the "Appraiser
                 Determination"). The Appraiser Determination shall be final and
                 binding on the Company and the Purchasers. If the Company

                                       8
<PAGE>

                 Determination and the Appraiser Determination differ by an
                 amount of 15% or less of the Company Determination, then the
                 costs of conducting the appraisal shall be borne equally by the
                 Company and the Purchasers; if the Company Determination is
                 greater than the Appraiser Determination by more than 15% of
                 the Company Determination, then the costs of conducting the
                 appraisal shall be borne entirely by the Purchasers; and if the
                 Appraiser Determination is greater than the Company
                 Determination by more than 15% of the Company Determination,
                 then the costs of conducting the appraisal shall be borne
                 entirely by the Company; provided that in each case costs
                 separately incurred by the Company and any Purchasers shall be
                 separately borne by them.

                 (c)   Anything in paragraph (a) to the contrary
          notwithstanding, the Company shall not be required to give effect to
          any adjustment in the Conversion Price unless and until the net effect
          of one or more adjustments (each of which shall be carried forward
          until counted toward adjustment), determined as above provided, shall
          have resulted in a change of the Conversion Price by at least 1%, and
          when the cumulative net effect of more than one adjustment so
          determined shall be to change the Conversion Price by at least 1%,
          such change in the Conversion Price shall thereupon be given effect.
          In the event that, at any time as a result of the provisions of this
          paragraph (b), the holder of this Note upon subsequent conversion
          shall become entitled to receive any shares of Capital Stock of the
          Company other than Common Stock, the number of such other shares so
          receivable upon conversion of this Note shall thereafter be subject to
          adjustment from time to time in a manner and on terms as nearly
          equivalent as practicable to the provisions contained herein.

                 (d)   In any case in which paragraph (a) requires that an
          adjustment as a result of any event is to become effective from and
          after a record date, the Company may elect to defer until after the
          occurrence of such event (i) issuing to the holder of this Note
          converted after such record date and before the occurrence of such
          event the additional shares of Common Stock issuable upon such
          conversion over and above the shares issuable on the basis of the
          Conversion Price in effect immediately prior to adjustment and (ii)
          paying to such holder any amount in cash in lieu of a fractional share
          of Common Stock.

                 (e)   If the Company shall take a record of the holders of its
          Common Stock for the purpose of entitling them to receive a dividend
          or other distribution, and shall thereafter and before the
          distribution to stockholders thereof legally abandon its plan to pay
          or deliver such dividend or distribution, then thereafter no
          adjustment in the number of

                                       9
<PAGE>

          shares of Common Stock issuable upon exercise of the right of
          conversion or in the Conversion Price then in effect shall be required
          by reason of the taking of such record.

                 (f)   Upon any adjustment of the Conversion Price or the number
          of shares of Common Stock issuable upon the Conversion of this Note, a
          certificate, signed by (i) the Company's president and chief financial
          officer or (ii) any independent firm of certified public accountants
          of recognized national standing the Company selects at its own
          expense, setting forth in reasonable detail the events requiring the
          adjustment and the method by which such adjustment was calculated,
          shall be mailed to the Purchaser at the address set forth in Section
          10.04 of the Note Purchase Agreement hereof and shall specify the
          adjusted Conversion Price and the number of shares of Common Stock
          issuable upon the Conversion of the Note after giving effect to the
          adjustment.

                 (g)   The Company shall not, by amendment of its Certificate of
          Incorporation or through any reorganization, recapitalization,
          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 hereunder by the Company, but shall at all times in good
          faith assist in the carrying out of all provisions of this Section 5
          and in the taking of all such action as may be necessary or
          appropriate in order to protect the rights of the Purchaser against
          impairment.

                 (h)   Except as otherwise provided herein, all sections of this
          Section 5 are intended to operate independently of one another. If an
          event occurs that requires the application of more than one section,
          all applicable sections shall be given independent effect.

          6.   Governing Laws.

          This Note shall be governed by, and construed in accordance with, the
laws of the State of New York in all respects, including all matters of
construction, validity and performance, without regard to the choice of law
provisions thereof.

                                       10
<PAGE>

          IN WITNESS WHEREOF, the Company has caused this Note to be signed on
its behalf, in its corporate name, by its duly authorized officer as an
instrument under seal, as of the day and year first above written.


                                          NAVISITE, INC.


                                          By:  /s/ Patricia Gilligan
                                              ------------------------
                                               Name: Patricia Gilligan
                                               Title: Chief Executive Officer

                                       11