Document:

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                                                                   Exhibit 10.51

                           CERTIFICATE OF DESIGNATIONS

                     VASCO DATA SECURITY INTERNATIONAL, INC.

                          Certificate of Designations,
                    Preferences and Rights of Preferred Stock
                     by Resolution of the Board of Directors
                    Providing for an Issue of 150,000 Shares
                          of Preferred Stock Designated
                     "SERIES C CONVERTIBLE PREFERRED STOCK"

I, MARIO HOUTHOOFT, President and Chief Executive Officer of VASCO DATA SECURITY
INTERNATIONAL, INC. (hereinafter referred to as the "CORPORATION"), a
corporation organized and existing under the General Corporation Law of the
State of Delaware (the "GENERAL CORPORATION LAW"), in accordance with the
provisions of Section 151 thereof, DO HEREBY CERTIFY:

That pursuant to authority conferred upon the Board of Directors of the
Corporation by the Certificate of Incorporation of said Corporation (hereinafter
referred to as the "CERTIFICATE OF INCORPORATION") the Board of Directors
adopted a resolution providing for the issuance of a series of Preferred Stock,
par value $.01 per share, of the Corporation to be designated "SERIES C
CONVERTIBLE PREFERRED STOCK", which resolution is as follows:

RESOLVED, that pursuant to the authority vested in the Board of Directors of the
Corporation by the Certificate of Incorporation, a series of Preferred Stock,
par value $.01 per share, of the Corporation be, and hereby is, created, to be
designated "SERIES C CONVERTIBLE PREFERRED STOCK" (hereinafter referred to as
the "SERIES C PREFERRED STOCK"), consisting of One Hundred Fifty Thousand
(150,000) shares, and, to the extent that the powers, preferences and relative
and other special rights, and the qualifications, limitations and restrictions
thereof, of the Series C Preferred Stock are not stated and expressed in the
Certificate of Incorporation, such powers, preferences and relative and other
special rights, and the qualifications, limitations and restrictions thereof,
are hereby fixed and stated to be as follows (all terms used herein which are
defined in the Certificate of Incorporation shall be deemed to have the meanings
provided therein):

The following terms shall have the meanings as set forth below:

                "BUSINESS DAY" means any day that is not a Saturday, a Sunday or
                a day on which banking institutions in New York, New York or
                Brussels, Belgium or the Nasdaq Stock Market are authorized or
                obligated by law, executive order or government decree to be
                closed.

                "DOLLARS" or "$" means the lawful currency of the United States
                of America.

                "OTHER SECURITIES" means any stock (other than Common Stock) and
                other securities of the Corporation or any other person
                (corporate or otherwise) which the record holders of the Series
                C Preferred Stock at any time shall be entitled to receive, or
                shall have received, upon the conversion of the Series C
                Preferred Stock, in lieu of or in addition to Common Stock, or
                which at any time shall be issuable or shall have been issued in
                exchange for or in replacement of Common Stock or Other
                Securities pursuant to Section 5 or otherwise.

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1    MANDATORY REDEMPTION OR CONVERSION

     1.1  Unless previously converted in accordance with the provisions of
          Section 2 hereof, on July [ ], 2004 (the "MANDATORY REDEMPTION DATE"),
          the Corporation shall redeem each outstanding share of Series C
          Preferred Stock for cash at a redemption price equal to the
          Liquidation Preference (as hereinafter defined), but only to the
          extent of funds of the Corporation legally available therefor pursuant
          to the General Corporation Law ("LEGALLY AVAILABLE FUNDS"). In
          addition, at the Corporation's option, or otherwise in the event that
          Legally Available Funds are insufficient to permit the Corporation to
          redeem some or all of the shares of Series C Preferred Stock for cash,
          the Corporation shall convert such shares of Series C Preferred Stock
          into shares of its Common Stock. The number of shares of Common Stock
          to be issued in connection with such conversion will be determined on
          the basis of a fraction, the numerator of which will be the
          Liquidation Preference and the denominator of which will be the lesser
          of (i) the average of the Market Prices (as defined in the next
          sentence) of the Common Stock for the period of 30 consecutive
          Business Days on which the Common Stock was traded ending on the
          Business Day immediately preceding the Mandatory Redemption Date,
          subject to a discount of five percent (5%) and (ii) the Liquidation
          Preference, such fraction multiplied by the number of shares of Series
          C Preferred Stock outstanding and unredeemed on the Mandatory
          Redemption Date. The "MARKET PRICE" of the Common Stock for any day
          means the last reported sales price, regular way, or, in case no sale
          takes place on such day, the average reported closing bid and asked
          prices, regular way, in either case as reported on the Nasdaq National
          Market.

     1.2  Immediately following such conversion, the rights of the holders of
          any converted shares of Series C Preferred Stock shall cease and the
          persons entitled to receive shares of Common Stock upon the conversion
          of such shares of Series C Preferred Stock shall be treated for all
          purposes as having been the owners of such shares of Common Stock,
          subject to Section 1.3 hereof. No payments or adjustments will be made
          upon the Mandatory Conversion Date on account of accrued and unpaid
          distributions, if any, on the shares of Series C Preferred Stock
          subject to such conversion.

     1.3  Upon conversion of the Series C Preferred Stock pursuant to Section
          1.1 hereof, the Corporation shall make such arrangements as it deems
          appropriate for (i) the issuance of certificates representing shares
          of Common Stock and (ii) payment of cash in lieu of any fractional
          shares of Common Stock in exchange for and contingent upon surrender
          of certificates representing shares of Series C Preferred Stock;
          provided that the Corporation shall give the holders of shares of
          Series C Preferred Stock notice of any such actions as the Corporation
          deems appropriate and, upon such surrender of their certificates
          representing Series C Preferred Stock, such holders shall be entitled
          to receive dividends declared and paid, if any, on such shares of
          Common Stock subsequent to the Mandatory Conversion Date.

2    CONVERSION AT THE OPTION OF HOLDER

     2.1  GENERAL Subject to and in compliance with the provisions of this
          Section 2, shares of Series C Preferred Stock may, at the option of
          any holder, be converted at any time and

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          from time to time (each, a "CONVERSION Date") into fully paid and
          nonassessable shares of Common Stock. The number of shares of Common
          Stock which a holder of shares of Series C Preferred Stock shall be
          entitled to receive upon conversion pursuant to this Section 2 shall
          be the product obtained by multiplying (i) the Applicable Conversion
          Rate (determined as provided in Section 2.2) by (ii) the number of
          shares of Series C Preferred Stock being converted on the Conversion
          Date.

     2.2  APPLICABLE CONVERSION RATE Subject to Section 5 hereof, the conversion
          rate in effect at any time for the conversion of the Series C
          Preferred Stock pursuant to this Section 2 (the "APPLICABLE CONVERSION
          RATE") shall be the lowest of the following:

          2.2.1  in the event that no shares of Common Stock have been issued or
                 sold during the period beginning on the date of issuance of the
                 Series C Preferred Stock and ending on the Conversion Date, the
                 quotient obtained by dividing (i) the Liquidation Preference of
                 the Series C Preferred Stock by (ii) $14.25;

          2.2.2  in the event that any shares of Common Stock were issued or
                 sold during the period beginning on the date of issuance of the
                 Series C Preferred Stock and ending on the Conversion Date at a
                 price per share of Common Stock exceeding $11.86 (the "UPPER
                 LIMIT"), the quotient obtained by dividing (i) the Liquidation
                 Preference of the Series C Preferred Stock by (ii) $14.25;

          2.2.3  in the event that any shares of Common Stock were issued or
                 sold during the period beginning on the date of issuance of the
                 Series C Preferred Stock and ending on the Conversion Date at a
                 price per share of Common Stock below or equal to the Upper
                 Limit but above $7.00 (the "LOWER LIMIT"), the quotient
                 obtained by dividing (i) the Liquidation Preference of the
                 Series C Preferred Stock by (ii) the difference between (a)
                 $14.25 and (b) a fraction (1) the numerator of which will be
                 the product of (A) the difference between $14.25 and the Upper
                 Limit and (B) the difference between the Upper Limit and the
                 price paid per share of Common Stock and (2) the denominator of
                 which will be the difference between the Upper Limit and the
                 Lower Limit; and

          2.2.4  in the event that any shares of Common Stock were issued or
                 sold during the period beginning on the date of issuance of the
                 Series C Preferred Stock and ending on the Conversion Date at a
                 price per share of Common Stock below or equal to the Lower
                 Limit, the quotient obtained by dividing (i) the Liquidation
                 Preference of the Series C Preferred Stock by (ii) $11.86.

          For purposes of this Section 2.2, the issuance or sale of Common Stock
          shall include the issuance and sale of shares of Common Stock as well
          as securities convertible into Common Stock ("CONVERTIBLE SECURITIES")
          and any rights or options to subscribe for, purchase or otherwise
          acquire Common Stock, and the price per share of Common Stock offered
          and sold for purposes of any calculations under this Section 2.2 shall
          be equal to the U.S. dollar equivalent of: (i) in the case of shares
          of Common Stock, the per share amount received or receivable by the
          Corporation as consideration for the issue and sale of such Common
          Stock, (ii) in the case of Convertible Securities, (a) the total
          amount received or receivable by the Corporation as consideration for
          the issue and sale of such Convertible Securities, plus the minimum
          aggregate amount of additional

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          consideration, if any, payable to the Corporation upon conversion or
          exchange thereof, divided by (b) the maximum number of shares of
          Common Stock issuable upon the conversion or exchange of such
          Convertible Securities and (iii) in the case of any rights or options
          to subscribe for, purchase or otherwise acquire stock, the total
          amount, if any, received or receivable by the Corporation as
          consideration for the granting of such rights or options, plus the
          minimum aggregate amount of additional consideration, if any, payable
          to the Corporation upon the exercise of such rights or options,
          divided by (b) the maximum number of shares of Common Stock issuable
          upon the exercise of such rights or options.

     2.3  EXERCISE OF CONVERSION PRIVILEGE To exercise its conversion privilege,
          a holder of shares of Series C Preferred Stock shall surrender the
          certificate(s) representing the shares being converted to the
          Corporation at its principal office, and shall give written notice to
          the Corporation at that office that such holder elects to convert such
          shares. Such notice shall also state the name or names (with address
          or addresses) in which the certificate(s) for shares of Common Stock
          issuable upon such conversion shall be issued. The certificate(s) for
          shares of Series C Preferred Stock surrendered for conversion shall be
          accompanied by proper assignment thereof to the Corporation or in
          blank. A notice hereunder shall be deemed to be given on the date it
          is dispatched, if by international airmail, domestic mail or overnight
          courier, or received, if sent by facsimile, telex or otherwise. The
          date when such written notice is received by the Corporation, together
          with the certificate(s) representing the shares of Series C Preferred
          Stock being converted, shall be the "CONVERSION DATE." Any voluntary
          conversion of shares of Series C Preferred Stock by any holder shall
          be for at least 100 shares of Common Stock. As promptly as practicable
          after the Conversion Date, the Corporation shall issue and shall
          deliver to the holder of the shares of Series C Preferred Stock being
          converted, or on its written order, such certificate(s) as it may
          request for the number of whole shares of Common Stock issuable upon
          the conversion of such shares of Series C Preferred Stock in
          accordance with the provisions of this Section 2, and cash, as
          provided in Section 2.4, in respect of any fraction of a share of
          Common Stock issuable upon such conversion.

     2.4  CASH IN LIEU OF FRACTIONAL SHARES No fractional shares of Common Stock
          or scrip representing fractional shares shall be issued upon the
          conversion of shares of Series C Preferred Stock pursuant to this
          Section 2. Instead of any fractional shares of Common Stock which
          would otherwise be issuable upon conversion of Series C Preferred
          Stock, the Corporation shall pay to the holder of the shares of Series
          C Preferred Stock which were converted a cash adjustment in respect of
          such fractional shares in an amount equal to the same fraction of the
          Market Price per share of the Common Stock at the close of business on
          the Conversion Date. The determination as to whether or not any
          fractional shares are issuable shall be based upon the aggregate
          number of shares of Series C Preferred Stock being converted at any
          one time by any holder thereof, not upon each share of Series C
          Preferred Stock being converted.

     2.5  PARTIAL CONVERSION In the event some but not all of the shares of
          Series C Preferred Stock represented by a certificate or certificates
          surrendered by a holder are converted, the Corporation shall execute
          and deliver to or on the order of the holder, at the expense

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          of the Corporation, a new certificate representing the number of
          shares of Series C Preferred Stock which were not converted.

     2.6  RESERVATION OF COMMON STOCK The Corporation shall at all times reserve
          and keep available out of its authorized but unissued shares of Common
          Stock, solely for the purpose of effecting the conversion of the
          shares of the Series C Preferred Stock, such number of its shares of
          Common Stock as shall from time to time be sufficient to effect the
          conversion of all outstanding shares of the Series C Preferred Stock,
          and if at any time the number of authorized but unissued shares of
          Common Stock shall not be sufficient to effect the conversion of all
          then outstanding shares of the Series C Preferred Stock, the
          Corporation shall take such action as may be necessary to increase its
          authorized but unissued shares of Common Stock to such number of
          shares as shall be sufficient for such purpose.

3    VOTING RIGHTS

     3.1  Each holder of outstanding shares of Series C Preferred Stock shall
          not be entitled to vote at any meeting of stockholders of the
          Corporation (or written actions of stockholders in lieu of meetings)
          with respect to any and all matters presented to the stockholders of
          the Corporation for their action or consideration, except as may be
          provided by law.

     3.2  Notwithstanding the foregoing, the Corporation shall not amend, alter
          or repeal preferences, rights, powers or other terms of the Series C
          Preferred Stock so as to affect adversely the Series C Preferred
          Stock, and may not create, authorize or issue shares of any class of
          stock ranking senior to or on parity with the Series C Preferred Stock
          without the written consent or affirmative vote of the holders of at
          least Sixty-Six and Two-Thirds percent (66 2/3%) of the then
          outstanding shares of Series C Preferred Stock, given in writing or by
          vote at a meeting, consenting or voting (as the case may be)
          separately as a class.

4    PRIORITY OF SERIES C PREFERRED STOCK IN THE EVENT OF LIQUIDATION OR
     DISSOLUTION

     In the event of any liquidation, dissolution, or winding up of the affairs
     of the Corporation, whether voluntary or otherwise, after payment or
     provision for payment of the debts and other liabilities of the
     Corporation, the holders of the Series C Preferred Stock shall be entitled
     to receive, out of the remaining net assets of the Corporation, the amount
     of One Hundred Dollars ($100.00) in cash for each share of Series C
     Preferred Stock, (the "LIQUIDATION PREFERENCE"), before any distribution of
     any kind shall be made to the holders of the Common Stock or any other
     stock ranking (as to any such distribution) junior to the Series C
     Preferred Stock. If, upon any liquidation, dissolution or winding up of the
     Corporation, the assets distributable among the holders of any series of
     Preferred Stock ranking (as to any such distribution) on a parity with the
     Series C Preferred Stock shall be insufficient to permit the payment in
     full to the holders of all such series of Preferred Stock of all
     preferential amounts payable to all such holders, then the entire assets of
     the Corporation thus distributable shall be distributed rateably among the
     holders of shares of Series C Preferred Stock and all series of Preferred
     Stock ranking (as to any such distribution) on a parity with the Series C
     Preferred Stock in proportion to the respective amounts that would be
     payable per share if such assets were sufficient to permit

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     payment in full. Except as otherwise provided in this Section 4, holders of
     Series C Preferred Stock shall not be entitled to any distribution in the
     event of liquidation, dissolution or winding up of the affairs of the
     Corporation. For the purposes of this Section 4, neither the voluntary
     sale, lease, conveyance, exchange or transfer (for cash, shares of stock,
     securities or other consideration) of all or substantially all the property
     or assets of the Corporation, nor the consolidation or merger of the
     Corporation with one or more other corporations, shall be deemed to be a
     liquidation, dissolution or winding up, voluntary or involuntary.

5    ADJUSTMENT FOR DIVIDENDS IN OTHER STOCK, PROPERTY, ETC.; R
     ECLASSIFICATION, ETC.

     In case at any time or from time to time after the date of issuance of the
     Series C Preferred Stock, the holders of Common Stock (or Other Securities)
     shall have received or (on or after the record date fixed for the
     determination of stockholders eligible to receive) shall have become
     entitled to receive without payment therefor

     (a)  other or additional stock or property (other than cash) by way of
          dividend, or

     (b)  any cash paid or payable (including, without limitation, by way of
          dividend other than a dividend payable out of earned surplus of the
          Corporation), or

     (c)  other or additional (or less) stock or property (including cash) by
          way of spin-off, split-up, recapitalization, combination of shares or
          similar corporate rearrangement,

     then, and in each such case the record holder of a share of Series C
     Preferred Stock, upon the conversion thereof as provided in Section 1 or 2,
     shall be entitled to receive the amount of stock and property (including
     cash in the cases referred to in subdivisions (b) and (c) of this Section
     5) which such record holder would hold on the date of such conversion if on
     the date of issuance of the Series C Preferred Stock such person had been
     the holder of record of the number of shares of Common Stock called for
     pursuant to the terms hereof and had thereafter, during the period from the
     date of issuance of the Series C Preferred Stock to and including the date
     of such conversion, retained such shares and all such other additional (or
     less) stock and property (including cash in the cases referred to in
     subdivisions (b) and (c) of this Section 5) receivable by such person as
     aforesaid during such period, giving effect to all adjustments called for
     during such period by Sections 2 and 5 hereof.

     In case the Corporation after the date of issuance of the Series C
     Preferred Stock shall (a) effect a reorganization, (b) consolidate or merge
     with any other person, or (c) transfer all or substantially all of its
     properties or assets to any other person under any plan or arrangement
     contemplating the dissolution of the Corporation, then, in each such case,
     the record holders of the Series C Preferred Stock, upon the conversion
     hereof as provided in Section 1 or 2 at any time after the consummation of
     such reorganization, consolidation or merger or the effective date of such
     dissolution, as the case may be, shall be entitled to receive (and the
     Corporation shall be entitled to deliver), in lieu of the Common Stock (or
     Other Securities) issuable upon such conversion prior to such consummation
     or such effective date, the stock and property (including cash) to which
     such record owner would have been entitled upon such consummation or in
     connection with such dissolution, as the case may be, if such record holder
     had so exercised such Series C Preferred Stock immediately prior thereto,
     all subject to further adjustment thereafter as provided in Section 2
     hereof.

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6    RANKING OF SERIES C PREFERRED STOCK

     With regard to rights to receive mandatory redemption payments and
     distributions upon liquidation, dissolution or winding up of the
     Corporation, the Series C Preferred Stock shall rank prior to any other
     equity securities of the Corporation.

7    REPLACEMENT OF SERIES C PREFERRED STOCK

     Upon receipt of evidence reasonably satisfactory to the Corporation of the
     loss, theft, destruction or mutilation of any certificate representing
     Series C Preferred Stock and, in the case of any such loss, theft or
     destruction, upon delivery of an indemnity agreement reasonably
     satisfactory in form and amount to the Corporation or, in the case of any
     such mutilation, upon surrender and cancellation of such certificate, the
     Corporation at its expense will execute and deliver, in lieu thereof, a new
     certificate.

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IN WITNESS WHEREOF, said VASCO DATA SECURITY INTERNATIONAL, INC. has caused this
Certificate to be signed by Mario Houthooft, its President and Chief Executive
Officer, this th day of July, 2000.

VASCO DATA SECURITY INTERNATIONAL, INC.

By:
   ---------------------------------------------
   Name:   Mario Houthooft
   Title:  President and Chief Executive Officer<PAGE>   1
                                                                     Exhibit 4.1

                               STOCK CERTIFICATE

NUMBER                                                                    SHARES
RSG

COMMON STOCK                                                   COMMON STOCK
THIS CERTIFICATE IS TRANSFERABLE                               CUSIP 760759 10 0
IN CHARLOTTE, NC AND NEW YORK, NY.

                             REPUBLIC SERVICES, INC.
              INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE

THIS CERTIFIES THAT                                                  SEE REVERSE
                                                                     FOR CERTAIN
                                                                     DEFINITIONS

IS THE OWNER OF

FULLY PAID AND NON-ASSESSABLE SHARES OF THE COMMON STOCK, PAR VALUE $.01, OF

Republic Services, Inc. transferable on the books of the Corporation in person
or by duly authorized attorney upon surrender of this Certificate properly
endorsed. This certificate and the shares evidenced hereby are issued under and
shall be subject to all of the provisions of the Certificate of Incorporation of
the Corporation and any amendments thereto, copies of which are on file with the
Corporation and the Transfer Agent, to all of which the holder by acceptance
hereof assumes. This Certificate is not valid until countersigned by the
Transfer Agent and registered by the Registrar.

Witness the facsimile seal of the Corporation and the facsimile signatures of
its duly authorized officers.

Dated:____________

/s/ Harris W. Hudson                                   /s/ H. Wayne Huizenga
------------------------                               ------------------------
VICE CHAIRMAN AND SECRETARY                            CHAIRMAN

                            [CORPORATE SEAL OMITTED]
                             REPUBLIC SERVICES, INC.
                                    SEAL 1996
                                    DELAWARE

Countersigned and Registered:

                           FIRST UNION NATIONAL BANK
                                (CHARLOTTE, NC)

                                                                  Transfer Agent
                                                                   and Registrar

By

                                                            Authorized Signature

<PAGE>   2

                            REPUBLIC SERVICES, INC.

THE COMPANY WILL FURNISH WITHOUT CHARGE TO EACH STOCKHOLDER WHO SO REQUESTS, THE
POWERS, DESIGNATIONS, PREFERENCES AND RELATIVE, PARTICIPATING, OPTIONAL OR OTHER
SPECIAL RIGHTS OF EACH CLASS OF STOCK OR SERIES THEREOF OF THE COMPANY AND THE
QUALIFICATIONS, LIMITATIONS OR RESTRICTIONS OF SUCH PREFERENCES AND/OR RIGHTS.
SUCH REQUEST MAY BE MADE TO THE OFFICE OF THE SECRETARY OF THE COMPANY.

The following abbreviations, when used in the inscription on the face of this
certificate, shall be construed as though they were written out in full
according to applicable laws or regulations:

<TABLE>
<CAPTION>
     <S>                                            <C>
      TEN COM - as tenants in common                UNIF GIFT MIN ACT-___________CUSTODIAN ___________
                                                                 (Cust)              (Minor)
      TEN ENT - as tenants by the entireties                   under Uniform Gifts to Minors
      JT TEN  - as joint tenants with rights of                       Act ______________
                surviorship and not as tenants                                (State)
                in common
</TABLE>

    Additional abbreviations may also be used though not in the above list.

    For value received, ______________ hereby sell, assign and transfer unto

PLEASE INSERT SOCIAL SECURITY OR OTHER
    IDENTIFYING NUMBER OF ASSIGNEE

---------------------------------------

---------------------------------------

--------------------------------------------------------------------------------
 (PLEASE PRINT OR TYPEWRITE NAME AND ADDRESS, INCLUDING ZIP CODE OF ASSIGNEE)

--------------------------------------------------------------------------------

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shares of the capital stock represented by the within Certificate, and do hereby
irrevocably constitute and appoint

_______________________________ Attorney to transfer the said stock on the books
of the within named Corporation with full power of substitution in the premises.

Dated:__________________

                  --------------------------------------------------------------
         NOTICE:  THE SIGNATURE TO THE ASSIGNMENT MUST CORRESPOND WITH THE NAME
                  AS WRITTEN UPON THE FACE OF THE CERTIFICATE IN EVERY
                  PARTICULAR, WITHOUT ALTERATION OR ENLARGEMENT OR ANY CHANGE
                  WHATEVER.

SIGNATURE(S)
GUARANTEED:
           ---------------------------------------------------------------------
           THE SIGNATURE(S) SHOULD BE GUARANTEED BY AN ELIGIBLE GUARANTOR
           INSTITUTION (BANKS, STOCKBROKERS, SAVINGS AND LOAN ASSOCIATIONS AND
           CREDIT UNIONS WITH MEMBERSHIP IN AN APPROVED SIGNATURE GUARANTEE
           MEDALLION PROGRAM), PURSUANT TO S.E.C. RULE 17Ad-15.

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