EXHIBIT 10.4(B)

                      STOCK PLEDGE AND SECURITY AGREEMENT
                      -----------------------------------

                           Dated as of March 6, 2000



          This STOCK PLEDGE AND SECURITY AGREEMENT ("this Agreement") is made as
of the date set forth above (the "date hereof") by MANUEL D. MEDINA, an
individual having an address at 2601 South Bayshore Drive, Coconut Grove,
Florida 33133 (the "Pledgor") to and in favor of OCEAN BANK, a Florida-chartered
bank (the "Bank").

                                  BACKGROUND
                                  ----------

          (A) The Pledgor and Terremark Fortune House #2, Ltd., a Florida
limited partnership, (collectively, the "Borrowers", each a "Borrower") are or
may become indebted to the Bank pursuant to and as evidenced by a Revolving
Promissory Note, dated on or about the date hereof, in the face principal amount
of U.S.$15,000,000 (together with any renewals and modifications thereof and
substitutions therefor, the "Note") and a related Credit Agreement, of even date
therewith, between the Borrowers and the Bank (as amended or restated from time
to time, the "Credit Agreement").

         (B) The Pledgor is the owner of 510,214 shares (the "Initial Shares")
of the common stock of Terremark Holdings, Inc., a Florida corporation,
evidenced by stock certificate no. 3-A (the "Initial Stock Certificate").

         (C) The Pledgor expects that, through a merger (the "Merger") conducted
pursuant to an Agreement and Plan of Merger, dated November 24, 1999, between
Terremark Holdings, Inc. and Amtec, Inc. (the "Merger Agreement"), the Initial
Shares will be converted into approximately 31,418,979 shares of Amtec, Inc.
which will be renamed Terremark Worldwide, Inc. (all shares of Amtec or
Terremark Worldwide, Inc. which the Pledgor receives or is entitled to receive
in connection with the Merger being the "Converted Shares," the Initial Shares
and the Converted Shares being collectively the "Shares," and Terremark
Holdings, Inc., Amtec, Inc. and Terremark Worldwide, Inc. each being an
"Issuer").

                                  AGREEMENTS
                                  ----------

          In consideration of the premises and other good and valuable
consideration (the receipt and adequacy of which are hereby acknowledged) and in
order to induce the Bank to make loans to the Borrowers, the Pledgor hereby
agrees as follows:

          ss.1. Pledge. The Pledgor hereby pledges to the Bank, and grants to
the Bank a security interest in, the following, whether now owned by the Pledgor
or hereafter acquired by it, and whether now or hereafter existing (the "Pledged
Collateral"): (a) the Shares, the Initial Stock Certificate and any and all
other instruments at any time evidencing any of the Shares, and all dividends,
interest, cash, instruments and other property from time to time received,
receivable or

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<PAGE>
EXHIBIT 10.4(B)

otherwise distributed in respect of or in exchange for any or all of the Shares;
(b) all stock and subscription rights to which the Pledgor is or may become
entitled on account of the Shares; (c) without limiting the generality of
clauses (b) and (d), all the Pledgor's rights under the Merger Agreement; and
(d) all proceeds of any of the foregoing.

          ss.2. Security for Obligations. This Agreement secures the payment of
any and all present or future obligations and liabilities of either or both of
the Borrowers to the Bank evidenced by or arising under the Note or the Credit
Agreement (whether for principal, interest, fees, expenses or otherwise), all
obligations of the Pledgor arising under this Agreement and all other
obligations or liabilities of the Borrower or the Pledgor to the Bank, whether
now existing or hereafter arising, whether joint or several and however
evidenced (all such obligations and liabilities referred to in this ss.2 being
the "Obligations").

          ss.3. Delivery of Pledged Collateral. The Stock Certificate and any
and each other certificate or instrument now or hereafter representing or
evidencing any part of the Pledged Collateral shall, when this Agreement is
executed or, if later, when such certificate or instrument is issued, be
delivered to the Bank at its office in Miami, Florida and shall thereafter be
held by or on behalf of the Bank pursuant hereto. Each such certificate or
instrument shall be in suitable form for transfer by delivery, or shall be
accompanied by duly executed instruments of transfer or assignment in blank, all
in form and substance satisfactory to the Bank. If and at any time after an
event described in ss.13 hereof or a default or an Event of Default (as
described or defined in the Credit Agreement) shall have occurred, the Bank
shall have the right, in its discretion and without notice to the Pledgor, to
transfer to or to register in the name of the Bank or any of its nominees any or
all of the Pledged Collateral and the Pledgor shall fully cooperate with any
such transfer or registration. In addition, the Bank shall have the right at any
time to exchange certificates or instruments representing or evidencing the
Pledged Collateral for certificates or instruments of smaller or larger
denominations. The Pledgor shall ensure that all Shares and other shares
included in the Pledged Collateral are certificated at all times.

         ss.4. Dividends, Profits and Other Distributions; Changes in Capital
Structure.
         (a) The Pledgor authorizes the Bank: (i) to receive any increase in or
dividends or profits on the Pledged Collateral and to hold the same as part of
the Pledged Collateral; and (ii) to receive any distribution upon dissolution
and liquidation of the Issuer, to surrender such Pledged Collateral or any part
thereof in exchange therefor, and to hold the net cash receipts from any such
distribution as part of the Pledged Collateral. If the Pledgor receives any such
dividend increase, profits or distribution, the Pledgor shall, promptly and
without the Bank's request, deliver the same promptly to the Bank to be held by
the Bank in the same manner as, and as part of, the Pledged Collateral. When
this Agreement is executed and before the Merger is consummated (and, upon the
Bank's request at any other time), the Pledgor shall instruct each Issuer to
make payment of any dividends or other distributions pertaining to the Pledged
Collateral directly to the Bank.

          (b) If during the term of this Agreement, any share dividend,
reclassification, readjustment, stock split or other change is declared or made
in the capital structure of the Issuer,

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<PAGE>
EXHIBIT 10.4(B)

all new, substituted, and additional shares, or other securities, issued by
reason of any such change shall be held by the Bank under the terms of this
Agreement in the same manner as, and as part of, the Pledged Collateral, but
nothing herein shall be construed as authorizing such change unless it is
pursuant to the Merger Agreement in the form heretofore furnished by the Pledgor
to the Bank.


          (c) If, during the term of this Agreement, subscription warrants or
any other rights or options are issued in connection with the Pledged
Collateral, such warrants, rights, and options shall be immediately assigned by
the Pledgor to the Bank, and, if exercised by the Pledgor, all new shares or
other securities so acquired by the Pledgor shall be immediately assigned to the
Bank to be held under the terms of this Agreement in the same manner as, and as
part of, the Pledged Collateral.

          (d) The Bank acknowledges that, in connection with the Merger, the
Bank may take and require whatever steps and measures it considers prudent to
ensure that there is no lapse in the perfection of its security interest in the
Shares and that its rights and interests hereunder are otherwise fully
protected.

          ss.5. Voting Rights. So long as no Event of Default (as defined or
described in the Credit Agreement) shall have occurred and be continuing, the
Pledgor shall be entitled to exercise or refrain from exercising any and all
voting and other consensual rights pertaining to the Pledged Collateral or any
part thereof for any purpose not detrimental to the Bank's rights hereunder and
not inconsistent with the terms of this Agreement; provided, however, that the
Pledgor shall not exercise or omit to exercise any such right if, in the Bank's
reasonable judgment, such action or omission (as the case may be) would have a
material adverse effect on the value of the Pledged Collateral or any part
thereof. However, upon the occurrence and during the continuance of an Event of
Default (as defined or described in the Credit Agreement), all rights of the
Pledgor to exercise or refrain from exercising the voting and other consensual
rights which it would otherwise be entitled to exercise pursuant to ss.5 shall,
upon notice to the Pledgor by the Bank, cease and all such rights shall
thereupon become vested in the Bank who shall thereupon have the sole right to
exercise or refrain from exercising such voting and other consensual.

         ss.6. Pledgor's Covenants. As long as any of the Obligations remain
unpaid, the Pledgor:

          (a) Shall defend the Pledged Collateral against the claims and demands
of all other parties; shall keep the Pledged Collateral free of all security
interests or other encumbrances, except the security interest created hereby;
and shall not sell, transfer, assign, deliver or otherwise dispose of any of the
Pledged Collateral or any interest therein without the prior written consent of
the Bank;


         (b) Shall notify the Bank promptly in writing of any change in the
Pledgor's address specified above;

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<PAGE>
EXHIBIT 10.4(B)

         (c) Shall pay all taxes, assessments and other charges of every nature
which may be levied or assessed against the Pledged Collateral;

          (d) Shall promptly secure from the board of directors or management of
the Issuer and deliver to the Bank whatever waivers or consents the Bank
considers would or might be necessary in connection with any future disposition
of the Pledged Collateral pursuant to ss.13 hereof; and

          (e)   Shall not permit any material amendment of the Merger Agreement.

         ss.7. Representations and Warranties. The Pledgor represents and
warrants (and, as long as any of the Obligations shall not have been paid in
full, shall be deemed continuously to warrant) to the Bank as follows:

          (a) The Pledgor is the sole legal and beneficial owner of all the
Pledged Collateral free and clear of any lien, security interest, option or
other charge or encumbrance except for the security interest created by this
Agreement and certain restrictions against sale included in the Merger
Agreement.

          (b) Except such as have heretofore been obtained, no authorization,
approval, or other action by, and no notice to or filing with, any governmental
authority or regulatory body or any other person (including any party to the
Merger Agreement or any related stock purchase agreement) is required either (i)
for the perfected pledge by the Pledgor of the Pledged Collateral pursuant to
this Agreement or the execution, delivery or performance of this Agreement by
the Pledgor or (ii) for the exercise by the Bank of the rights provided for in
this Agreement or the remedies in respect of the Pledged Collateral pursuant to
this Agreement.

          (c) The pledge of the Pledged Collateral pursuant hereto creates a
valid and perfected, first-priority security interest in the Pledged Collateral
securing payment of the Obligations under all applicable or potentially
applicable law.

          (d) The Pledgor has received adequate consideration and equivalent
value for executing and delivering this Agreement, will not be rendered
insolvent thereby and will not be left undercapitalized thereby. This Agreement
is the legal, valid and binding obligation of the Pledgor enforceable against it
in accordance with its terms.

          (e) The Initial Shares are, and, upon their issuance the Converted
Shares will be, validly issued, fully paid and non-assessable.

          ss.8. Further Assurances. The Pledgor agrees that at any time and from
time to time, at the expense of the Pledgor, the Pledgor will promptly execute
and deliver all further instruments and documents, and take all further action,
that may be necessary or desirable, or that the Bank may reasonably request, in
order to perfect or protect any security interest granted or purported to be

                                     -4-
<PAGE>
EXHIBIT 10.4(B)

granted hereby or to enable the Bank to exercise and enforce its rights and
remedies hereunder with respect to any of the Pledged Collateral.

          ss.9. Transfers and Other Liens. The Pledgor agrees that it will not
(i) sell or otherwise dispose of, or grant any option with respect to, any of
the Pledged Collateral, or (ii) create or permit to exist any lien, security
interest, or other charge or encumbrance upon or with respect to any of the
Pledged Collateral, except for the security interest created under this
Agreement.

         ss.10. Bank Appointed Attorney-in-Fact. The Pledgor hereby appoints the
Bank the Pledgor's attorney-in-fact, with full authority in the place and stead
of the Pledgor and in the name of the Pledgor or otherwise, from time to time in
the Bank's discretion to take any action and to execute any instrument which the
Bank may deem necessary or advisable to accomplish the purposes of this
Agreement, including, without limitation, to receive, indorse and collect all
instruments made payable to the Pledgor representing any dividend, interest
payment or other distribution in respect of the Pledged Collateral or any part
thereof and to give full discharge for the same and to exchange the Shares for
shares of Amtec, Inc., Terremark Worldwide, Inc. or any other company (pursuant
to the Merger Agreement or otherwise).

          ss.11. Bank May Perform. If the Pledgor fails to perform any agreement
contained herein and the applicable grace period, if any, expires, the Bank may
itself perform, or cause performance of, such agreement, and the reasonable
expenses of the Bank incurred in connection therewith shall be payable by the
Pledgor under ss.15 hereof.

          ss.12. Reasonable Care. The Bank shall be deemed to have exercised
reasonable care in the custody and preservation of the Pledged Collateral in its
possession if the Pledged Collateral is accorded treatment substantially equal
to that which the Bank accords its own property, it being understood that the
Bank shall not have any responsibility for (i) ascertaining or taking action
with respect to calls, conversions, exchanges, maturities, tenders or other
matters relative to any of the Pledged Collateral, whether or not the Bank has
or is deemed to have knowledge of such matters, or (ii) taking any necessary
steps to preserve rights against any parties with respect to any of the Pledged
Collateral.

          ss.13. Remedies upon Default. If and at any time after the Borrower
fails to make when due any payment of principal of or interest on the Note, an
Event of Default as defined or described in the Credit Agreement occurs, the
Pledgor defaults in the performance of any covenant or warranty hereunder, or
any representation of the Pledgor to the Bank proves to be inaccurate or
misleading:

          (a) The Bank may exercise in respect of the Pledged Collateral, in
addition to other rights and remedies provided for herein or otherwise available
to it, all the rights and remedies of a secured party on default under the
Uniform Commercial Code (the "Code") in effect in the State of Florida at that
time, and the Bank may also, without notice except as specified below, sell the
Pledged Collateral or any part thereof in one or more parcels at public or
private sale, at any exchange, broker's board or at any of the Bank's offices or
elsewhere, for cash, on credit or for future

                                     -5-
<PAGE>
EXHIBIT 10.4(B)

delivery, and upon such other terms as the Bank may deem commercially
reasonable. To the maximum extent permitted by applicable law, the Pledgor
waives any right it may have to notification of the sale or other disposition of
the Pledged Collateral. The Pledgor agrees that, to the extent notification of
sale shall be required by law and cannot be waived, at least seven calendar
days' notice to the Pledgor of the time and place of any public sale or the time
after which any private sale is to be made shall constitute reasonable
notification. The Bank shall not be obligated to make any sale of Pledged
Collateral regardless of notification of sale having been given. The Bank may
adjourn any public or private sale from time to time by announcement at the time
and place fixed therefor, and such sale may, without further notice, be made at
the time and place to which it was so adjourned.

          (b) Any cash held by the Bank as Pledged Collateral and all cash
proceeds received by the Bank in respect of any sale of, collection from, or
other realization upon all or any part of the Pledged Collateral may, in the
discretion of the Bank, be held by the Bank as collateral for, and/or then or at
any time thereafter applied (after payment of any amounts payable to the Bank
pursuant to ss.15) in whole or in part by the Bank against, all or any part of
the Obligations in such order as the Bank shall elect.

         ss.14. Registration Rights. If the Bank determines to exercise its
right to sell all or any of the Pledged Collateral pursuant to ss.13, the
Pledgor agrees that, upon request of the Bank, the Pledgor will, at its own
expense, with regard to any Converted Shares:

          (a) execute and deliver, and cause each issuer of the Pledged
Collateral contemplated to be sold and the directors and officers thereof to
execute and deliver, all such instruments and documents, and do or cause to be
done all such other acts and things, as may be necessary or, in the opinion of
the Bank, advisable to register such Pledged Collateral under the provisions of
the Securities Act of 1933, as from time to time amended (the "Securities Act")
, and to cause the registration statement relating thereto to become effective
and to remain effective for such period as prospectuses are required by law to
be furnished, and to make all amendments and supplements thereto and to the
related prospectus which, in the opinion of the Bank, are necessary or
advisable, all in conformity with the requirements of the Securities Act and the
rules and regulations of the Securities and Exchange Commission applicable
thereto;

          (b) use its best efforts to qualify the Pledged Collateral under state
securities or "Blue Sky" laws and to obtain all necessary governmental approvals
for the sale of the Pledged Collateral, as requested by the Bank;

          (c) cause each such issuer to make available to its security holders,
as soon as practicable, an earnings statement which will satisfy the provisions
of Section 11(a) of the Securities Act; and


                                     -6-
<PAGE>
EXHIBIT 10.4(B)

          (d) do or cause to be done all such other acts and things as may be
necessary to make such sale of the Pledged Collateral or any part thereof valid
and binding and in compliance with applicable law.

The Pledgor further acknowledges the impossibility of ascertaining the amount of
damages which would be suffered by the Bank by reason of the failure by the
Pledgor to perform any of the covenants contained in this ss.14 and,
consequently, agrees that, if the Pledgor shall fail to perform any of such
covenants, it shall pay, as liquidated damages and not as a penalty, an amount
equal to the value of the Pledged Collateral on the date the Bank shall demand
compliance with this ss.14.

          ss.15. Expenses. The Pledgor shall, upon demand, pay to the Bank the
amount of any and all reasonable expenses, including the reasonable fees and
expenses of its counsel and of any experts and agents, which the Bank may incur
in connection with: (i) the negotiation, preparation and signing of the Note and
this Agreement; (ii) the perfection of the Bank's security interest in the
Pledged Collateral; (iii) the custody or preservation of, or the sale of,
collection from, or other realization upon, any of the Pledged Collateral; (iv)
the exercise or enforcement of any of the rights of the Bank hereunder; or (v)
the failure by the Pledgor to perform or observe any of the provisions hereof.

          ss.16. Amendments, Etc. No amendment or waiver of any provision of
this Agreement nor consent to any departure by the Pledgor herefrom, shall in
any event be effective unless the waiver or consent is in writing and signed by
the Bank, and then such waiver or consent shall be effective only in the
specific instance and for the specific purpose for which given.

          ss.17. Addresses for Notices. All notices, demands or other
communications to the Pledgor in connection herewith shall be sufficiently given
if mailed, hand-delivered or telecopied to the Pledgor at the address specified
at the head of this Agreement (or, if no address is specified there, the address
appearing in the Bank's records) or such other place of which the Pledgor may
from time to time notify the Bank. Any such mailed notice shall be deemed to
have been given when placed in the United States mails and any such telecopied
or hand-delivered notice shall be deemed to have been given when received or
rejected.

          ss.18. Continuing Security Interest; Transfer of Note. This Agreement
shall create a continuing security interest in the Pledged Collateral and shall
(i) remain in full force and effect until payment in full of the Obligations and
its release in writing by the Bank and thereafter as long as any payment of or
recovery against or with respect to the Obligations might, in the Bank's
judgment, be rescinded or otherwise required to be returned by the Bank for any
reason, including the bankruptcy, insolvency or reorganization of the Borrower,
(ii) be binding upon the Pledgor, his heirs, personal representatives,
successors and assigns, and (iii) inure to the benefit of the Bank and its
successors, transferees and assigns. Without limiting the generality of the
foregoing clause (iii), the Bank may assign or otherwise transfer any of the
Obligations to any other person or entity, and such other person or entity shall
thereupon become vested with all the benefits in respect thereof granted to the
Bank herein or otherwise.

                                     -7-
<PAGE>
EXHIBIT 10.4(B)

         ss.19. Security Interest Absolute. All rights of the Bank and
assignment and security interest hereunder, and all obligations of the Pledgor
hereunder, shall be absolute and unconditional irrespective of:

         (i) any lack of validity or enforceability of any other agreement or
         instrument relating to or giving rise to any of the Obligations;

         (ii) any change in the time, manner or place of payment of, or in any
         other term of, all or any of the Obligations, or any other amendment or
         waiver of or any consent to any departure from any other agreement or
         instrument giving rise to any of the Obligations;

         (iii) any exchange, release or nonperfection of any other collateral,
         or any release or amendment or waiver of or consent to departure from
         any guaranty, for all or any of the Obligations; or

         (iv) any other circumstance which might otherwise constitute a defense
         available to, or a discharge of, a third party pledgor.

         ss.20. Governing Law. This Agreement shall be governed by and construed
in accordance with the laws of the State of Florida, without regard to any
conflict-of-law rule or principle that would give effect to the laws of another
jurisdiction.

         ss.21. Consent to Jurisdiction.

          (a) The Pledgor hereby irrevocably submits to the non-exclusive
jurisdiction of any Florida State or Federal court sitting in Miami-Dade County,
Florida or Broward County, Florida over any action or proceeding arising out of
or relating to this Agreement. The Pledgor hereby irrevocably waives, to the
fullest extent it may effectively do so, the defense of an inconvenient forum to
the maintenance of any such action or proceeding. The Pledgor hereby irrevocably
appoints Brian Goodkind, Esq., 2601 South Bayshore Drive, PH-1B, Coconut Grove,
Florida 33133, as its agent to accept and forward such service to the Pledgor of
copies of the summons and complaint and any other process which may be served in
any such action or proceeding. As an alternative method of service, the Pledgor
also irrevocably consents to the service of any and all process in any such
action or proceeding by the mailing of a copy of such process to the Pledgor at
its address as set forth below. The Pledgor agrees that a final judgment in any
such action or proceeding shall be conclusive and may be enforced in other
jurisdictions by suit on the judgment or in any other manner provided by law.

          (b) Nothing in this ss.21 shall affect the right of the Bank to serve
legal process in any other manner permitted by law or affect the right of the
Bank to bring any action or proceeding against the Pledgor or its property in
the courts of other jurisdictions.


                                     -8-
<PAGE>
EXHIBIT 10.4(B)

          (c) To the extent that the Pledgor has or hereafter may acquire any
immunity from jurisdiction of any court or from any legal process (whether
through service or notice, attachment in aid of execution, attachment prior to
judgment, execution or otherwise) with respect to itself or its property, the
Pledgor hereby irrevocably waives such immunity in respect of its obligations
under this Agreement.

         ss.22. WAIVER OF JURY TRIAL. THE PLEDGOR AND (BY ACCEPTANCE HEREOF) THE
BANK EACH WAIVES ANY RIGHT IT MAY HAVE TO A JURY TRIAL IN ANY ACTION, PROCEEDING
OR COUNTERCLAIM RELATING TO THIS AGREEMENT.

          IN WITNESS WHEREOF, the Pledgor has duly executed and delivered this
Agreement as of the date first above written.


Witnessed by:

___________________________
                                ___________________________________________
                                Manuel D. Medina
___________________________


STATE OF FLORIDA                  )
                                  )   SS:
COUNTY OF MIAMI-DADE              )


         The foregoing instrument was acknowledged before me this_____ day of
_______________, 2000 by Manuel D. Medina. He is personally known to me or has
produced __________________________________ as identification.

                                  ________________________________________
                                  Notary Public,__________________________
                                  Print Name: ____________________________


My commission expires:              (SEAL)

                                     -9-