Document:

EXHIBIT 4.3
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              NEITHER THE WARRANTS REPRESENTED BY THIS CERTIFICATE
                NOR THE SECURITIES ISSUABLE UPON EXERCISE HEREOF
             HAVE BEEN REGISTERED UNDER THE SECURITIES ACT OF 1933,
                  AS AMENDED, OR UNDER ANY STATE SECURITIES LAW
                           AND MAY NOT BE TRANSFERRED
                 IN VIOLATION OF SUCH ACT OR LAWS, THE RULES AND
                    REGULATIONS THEREUNDER OR THE PROVISIONS
                           OF THIS WARRANT CERTIFICATE

                                                              __________________

            WARRANTS TO PURCHASE AN AGGREGATE OF ____________ SHARES
                               OF COMMON STOCK OF
                       NETWORK-1 SECURITY SOLUTIONS, INC.
             (INCORPORATED UNDER THE LAWS OF THE STATE OF DELAWARE)

                                    ISSUED TO
                         _____________________________

                             DATED: _______________

                  THIS IS TO CERTIFY that, for value received, _______________ ,
or his or its registered assigns (herein collectively referred to as the
"Warrantholder"), is entitled to the number of Warrants (the "Warrants") set
forth above, each of which represents the right, upon the due exercise hereof,
at any time commencing on the date hereof (the "Commencement Date") and ending
on _______________ (the "Expiration Date"), to purchase from Network-1 Security
Solutions, Inc., a Delaware corporation (the "Company"), one share of common
stock, par value $.01 per share (the "Common Stock"), of the Company upon
surrender hereof, with the form of election to purchase included herein (the
"Election to Purchase") completed and duly executed, at the office of the
Company, and upon simultaneous payment therefor of an exercise price per share
equal to the Purchase Price (as defined in Section 1 below) in cash and/or check
payable to the order of the Company. The number of shares of Common Stock
issuable upon exercise of the Warrants (individually, a "Share" and
collectively, the "Shares") and the Purchase Price therefor are subject to
adjustment as provided herein.

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         1. Purchase Price

         The purchase price for the Shares purchasable hereunder (the "Purchase
Price") shall be equal to $__________ per Share, subject to adjustment as
hereinafter described.

         2. Definition of Market Price

         Unless otherwise provided herein, for purposes of any computations made
hereunder, "Market Price" per share of Common Stock on any date shall be: (i) if
the Common Stock is listed or admitted for trading on any national securities
exchange, the last reported sales price as reported on such national securities
exchange; (ii) if the Common Stock is not listed or admitted for trading on any
national securities exchange, the average of the last reported closing bid and
asked quotation for the Common Stock as reported on the Nasdaq Stock Market's
National Market ("NNM") or a similar service if NNM is not reporting such
information; (iii) if the Common Stock is not listed or admitted for trading on
any national securities exchange or NNM or quoted by the Nasdaq Stock Market's
SmallCap Market ("NSM") or a similar service, the average of the last reported
bid and asked quotation for the Common Stock as quoted by a market maker in the
Common Stock (or if there is more than one market maker, the bid and asked
quotation shall be obtained from two market makers and the average of the lowest
bid and highest asked quotation shall be the "Market Price"); or (iv) if the
Common Stock is not listed or admitted for trading on any national securities
exchange or NNM or quoted by NSM and there is no market maker in the Common
Stock, the fair market value of such shares as determined in good faith by the
Board of Directors of the Company.

         3. Transfer

         The Warrants may not be transferred, sold or assigned except to, in
whole or in part (i) any entity controlled by, or under common control with, the
Warrantholder, (ii) the spouse, lineal descendants, estate or a trust for the
benefit of any of the foregoing, or (iii) by operation of law.

         4. Issuance of Shares

         Subject to the restrictions set forth in Section 5 below, upon
surrender of the Warrants and payment of the Purchase Price as aforesaid, the
Company shall issue and deliver with all reasonable dispatch the certificate(s)
for the Shares to or upon the written order of the Warrantholder and in such
name or names as the Warrantholder may designate. Such certificate(s) shall
represent the number of Shares issuable upon the exercise of the Warrants,
together with a cash amount in respect of any fraction of a Share otherwise
issuable upon such exercise.

         Certificates representing the Shares shall be deemed to have been
issued and the person so designated to be named therein shall be deemed to have
become a holder of record of such Shares as of the date of the surrender of the
Warrants and payment of the Purchase Price as aforesaid; notwithstanding that
the transfer books for the Shares or other classes of stock purchasable upon the
exercise of the Warrants shall then be closed or the certificate(s) for the
Shares in respect

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of which the Warrants is then exercised shall not then have been actually
delivered to the Warrantholder. As soon as practicable after each such exercise
of the Warrants, the Company shall issue and deliver the certificate(s) for the
Shares issuable upon such exercise, registered as requested. The Warrants shall
be exercisable, at the election of the registered holder hereof, either as an
entirety or from time to time for part of the number of Shares specified herein,
but in no event shall fractional Shares be issued with regard to the exercise of
the Warrants. In the event that only a portion of the Warrants is exercised at
any time prior to the close of business on the Expiration Date, a new warrant
certificate shall be issued to the Warrantholder for the remaining number of
Shares purchasable pursuant hereto. The Company shall cancel the Warrants when
they are surrendered upon exercise.

         Prior to due presentment for registration of transfer of the Warrants,
the Company shall deem and treat the Warrantholder as the absolute owner of the
Warrants (notwithstanding any notation of ownership or other writing on this
warrant certificate made by anyone other than the Company) for the purpose of
any exercise hereof or any distribution to the Warrantholder and for all other
purposes, and the Company shall not be affected by any notice to the contrary.

         5. Payment of Expenses, Taxes, etc. upon Exercise

         The Company shall pay all documentary stamp taxes, if any, attributable
to the initial issuance of the Shares issuable upon the exercise of the
Warrants; provided, however, that the Company shall not be required to pay any
tax or taxes which may be payable in respect of any transfer involved in the
issue or delivery of any certificates for Shares in a name other than that of
the Warrantholder upon the exercise of the Warrants, and in such case the
Company shall not be required to issue or deliver any certificates for Shares
until or unless the person or persons requesting the issuance have paid to the
Company the amount of such tax or have established to the Company's satisfaction
that such tax has been paid or is not required to be paid.

         6. Lost, Stolen, or Mutilated Warrant Certificate

         In case this warrant certificate shall be mutilated, lost, stolen or
destroyed, the Company shall issue and deliver, in exchange and substitution for
and upon cancellation of the mutilated warrant certificate, or in lieu of and
substitution for the warrant certificate lost, stolen or destroyed, a new
warrant certificate of like tenor and representing an equivalent number of
Shares purchasable upon exercise, but only upon receipt of evidence reasonably
satisfactory to the Company of such loss, theft or destruction of such warrant
certificate and reasonable indemnity, if requested, also reasonably satisfactory
to the Company. No bond or other security shall be required from the original
Warrantholder in connection with the replacement by the Company of a lost,
stolen or mutilated warrant certificate.

<PAGE>

         7. Covenants of Company

         (a) The Company shall at all times through the Expiration Date reserve
and keep available, out of its aggregate authorized but unissued shares of
Common Stock, the number of Shares deliverable upon the exercise of the
Warrants.

         (b) Before taking any action which would cause an adjustment pursuant
to the terms set forth herein reducing the portion of the Purchase Price
attributable to the Shares below the then par value (if any) of such Shares, the
Company shall take any corporate action which may, in the opinion of its counsel
(which may be counsel regularly engaged by the Company), be necessary in order
that the Company may validly and legally issue fully paid and nonassessable
Shares at the Purchase Price as so adjusted.

         (c) The Company covenants that all Shares issued upon exercise of the
Warrants shall, upon issuance in accordance with the terms hereof, be fully paid
and nonassessable and free from all pre-emptive rights and taxes, liens, charges
and security interests created by the Company with respect to the issuance and
holding thereof.

         (d) For so long as the Warrants are outstanding, the Company shall
notify the Warrantholder not less than 30 days prior to any cash dividend being
paid to the holders of Common Stock.

         8. Rights Upon Expiration

         Unless the Warrants are surrendered and payment made for the Shares as
herein provided before the close of business on the Expiration Date, this
warrant certificate will become wholly void and all rights evidenced hereby will
terminate after such time.

         9. Exchange of Warrant Certificate

         Subject to the provisions of Section 3 above, this warrant certificate
may be exchanged for a number of warrant certificates of the same tenor as this
warrant certificate for the purchase in the aggregate of the same number of
Shares of the Company as are purchasable upon the exercise of this warrant
certificate, upon surrender hereof at the office of the Company with written
instructions as to the denominations of the warrant certificates to be issued in
exchange.

         10. Adjustment for Certain Events

         (a) In case the Company shall at any time after the date the Warrants
are first issued (i) declare a dividend on the Common Stock payable in shares of
the Company's capital stock (whether in shares of Common Stock or of capital
stock of any other class), (ii) subdivide the outstanding Common Stock, (iii)
reverse split the outstanding Common Stock into a smaller number of shares, or
(iv) issue any shares of the Company's capital stock in a reclassification of
the Common

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Stock (including any such reclassification in connection with a consolidation or
merger in which the Company is the continuing corporation), then, in each case,
the Purchase Price in effect at the time of the record date for such dividend or
of the effective date of such subdivision, reverse split or reclassification,
and/or the number and kind of shares of capital stock issuable upon exercise of
the Warrants on such date, shall be proportionately adjusted so that the holder
of any Warrant exercised after such time shall be entitled to receive the
aggregate number and kind of securities which, if such Warrant had been
exercised immediately prior to such date, such holder would have owned upon such
exercise and been entitled to receive by virtue of such dividend, subdivision,
reverse split or reclassification. Such adjustment shall be made successively
whenever any event listed above shall occur.

         (b) In case the Company shall fix a record date for the making of a
distribution to all holders of Common Stock (including any such distribution
made in connection with a consolidation or merger in which the Company is the
continuing corporation) of evidences of indebtedness or assets (other than cash
dividends or cash distributions payable out of earnings, consolidated earnings,
if the Company shall have one or more subsidiaries, or earned surplus, or
dividends payable in Common Stock) or rights, options or warrants to subscribe
for or purchase Common Stock, then, in each case, the Purchase Price per Share
to be in effect after such record date shall be determined by multiplying the
Purchase Price in effect immediately prior to such record date by a fraction, of
which the numerator shall be the current Market Price for a share of Common
Stock on such record date less the fair market value of the portion of the
assets or evidences of indebtedness so to be distributed or of such subscription
rights, options or warrants applicable to one share of Common Stock, and of
which the denominator shall be the current Market Price for a share of Common
Stock. In the event that the Company and the Warrantholder cannot agree as to
such fair market value, such determination of fair market value shall be made by
an appraiser who shall be mutually selected by the Company and the
Warrantholder, and the reasonable costs of such appraiser shall be borne by the
Company. Such adjustment shall be made successively whenever such a record date
is fixed, and in the event that such distribution is not so made, the Purchase
Price shall again be adjusted to be the Purchase Price which would then be in
effect if such record date had not been fixed.

         (c) No adjustment in the Purchase Price shall be required unless such
adjustment would require a decrease of at least one cent ($0.01) in such price;
provided, however, that any adjustment which by reason of this Section 10(c) is
not required to be made shall be carried forward and taken into account in any
subsequent adjustment. All calculations under this Section 10 shall be made to
the nearest cent or to the nearest one-hundredth of a share, as the case may be,
but in no event shall the Company be obligated to issue fractional shares of
Common Stock or fractional portions of any securities upon the exercise of the
Warrants.

<PAGE>

         (d) In the event that at any time, as a result of an adjustment made
pursuant to Section 10 hereof, the holder of any Warrant thereafter exercised
shall become entitled to receive any shares of capital stock or warrants or
other securities of the Company other than the Shares, thereafter the number of
such other shares of capital stock or warrants or other securities so receivable
upon exercise of this Warrant shall be subject to adjustment from time to time
in a manner and on terms as nearly equivalent as practicable to the provisions
with respect to the Shares contained in this Section 10, and the provisions of
this warrant certificate with respect to the Shares shall apply, to the extent
applicable, on like terms to any such other shares of capital stock or warrants
or other securities.

         (e) Upon each adjustment of the Purchase Price as a result of
calculations made in this Section 10, each Warrant outstanding immediately prior
to the making of such adjustment shall thereafter evidence the right to
purchase, at the adjusted Purchase Price, that number of Shares (calculated to
the nearest hundredth), obtained by (i) multiplying the number of Shares
purchasable upon exercise of a Warrant immediately prior to such adjustment of
the Purchase Price by the Purchase Price in effect immediately prior to such
adjustment and (ii) dividing the product so obtained by the Purchase Price in
effect immediately after such adjustment of the Purchase Price.

         (f) In case of any capital reorganization of the Company or of any
reclassification of the Common Stock (other than a change in par value or from a
specified par value to no par value or from no par value to a specified par
value or as a result of subdivision or combination) or in case of the
consolidation of the Company with, or the merger of the Company into, any other
corporation (other than a consolidation or merger in which the Company is the
continuing corporation) or of the sale of the properties and assets of the
Company as, or substantially as, an entirety, each Warrant shall, after such
reorganization, reclassification, consolidation, merger or sale, be exercisable,
upon the terms and conditions specified herein, for the number of shares of
Common Stock or other capital stock or warrants or other securities or property
to which a holder of the number of shares of Common Stock purchasable (at the
time of such reorganization, reclassification, consolidation, merger or sale)
upon exercise of such Warrant would have been entitled upon such reorganization,
reclassification, consolidation, merger or sale; and in any such case, if
necessary, the provisions set forth in this Section 10(f) with respect to the
rights and interests thereafter of the registered holders of all Warrants shall
be appropriately adjusted so as to be applicable, as nearly as may reasonably
be, to any shares of Common Stock or other capital stock or warrants or other
securities or property thereafter deliverable on the exercise of the Warrants.
The subdivision, reverse split or combination of shares of Common Stock at any
time outstanding into a greater or lesser number of shares shall not be deemed
to be a reclassification of the Common Stock for the purposes of this Section
10(f).

         (g) In any case in which this Section 10 shall require that an
adjustment in the Purchase Price be made effective as of a record date for a
specified event, the Company may elect to defer until the occurrence of such
event issuing to the Warrantholder, if such Warrantholder exercised any Warrant
after such record date, shares of capital stock or warrant or other securities
of the Company, if any, issuable upon such exercise over and above the Shares
issuable, on the basis of the Purchase Price in effect prior to such adjustment;
provided, however, that the Company shall

<PAGE>

deliver to the holder a due bill or other appropriate instrument evidencing such
holder's right to receive such shares of capital stock or warrants or other
securities upon the occurrence of the event requiring such adjustment.

         11. Piggyback Registration Rights.

         (i) The Warrantholder is hereby granted the right to "piggyback" the
Shares on each registration statement filed by the Company so long as the
registration form to be used is suitable for the registration of the Shares (a
"Piggyback Registration") (it being understood that the Form S-8 and Form S-4
may not be used for such purposes), all at the Company's cost and expense
(except commissions or discounts) PROVIDED, HOWEVER, that this paragraph (a)
shall not apply to any Shares if such Shares may then be sold within a six (6)
month period under Rule 144 (assuming the Warrantholder's compliance with the
provisions of the Rule) and the Company delivers an opinion to that effect to
the transfer agent; and PROVIDED, FURTHER, that if the offering with respect to
which a registration statement is filed is an underwritten primary or secondary
offering of the Company's securities and the managing underwriter advises the
Company in writing that in its opinion the number of securities requested to be
included in such registration exceeds the number that can be sold in such
offering without adversely affecting such underwriter's ability to effect an
orderly distribution of such securities or otherwise adversely affecting such
offering (including, without limitation, causing a diminution in the offering
price of the Company's securities) the Company will include such registration
statement: (i) first, the securities being sold for the account of the Company;
(ii) second, the number of Registrable Securities to be included that, in the
opinion of such underwriter, can be sold pro rata among the respective holders
of such securities on the basis of the amount of shares then owned by each such
holder. The Company shall give the Warrantholder at least fifteen (15) days
written notice of the intended filing date of any registration statement, other
than a registration statement filed on Form S-4 or Form S-8 and the
Warrantholder shall have seven (7) days after such receipt of such notice to
notify the Company of its intent to include the Shares in the registration
statement. The Company shall keep any registration statement onto which the
Warrantholder has "piggybacked" the Shares current and effective for a period of
up to 150 days from the date on which the Warrantholder is first entitled to
sell the total number of his Registrable Securities registered thereunder.

         (ii) If, at any time after giving written notice of its intention to
register any securities and prior to the effective date of the registration
statement filed in connection with such registration, the Company shall
determine for any reason not to register or to delay registration of such
securities, the Company may, at its election, give written notice of such
determination to Warrantholder (as well as all other holders of the Registrable
Securities) and (i) in the case of a determination not to register, shall be
relieved of its obligation to register the Shares in connection with such
abandoned registration and (ii) in the case of a determination to delay such
registration of its securities, shall be permitted to delay the registration of
such Shares for the same period as the delay in registering such other Company
securities.

<PAGE>

         (iii) The Company shall indemnify and hold harmless the Warrantholder
with respect to Shares to be sold pursuant to any Registration Statement
hereunder and any of such holder's officer's, directors, employees, agents,
partners, legal counsel and accountants, and each person, if any, who controls
each of the foregoing within the meaning of Section 15 of the Securities Act or
Section 20(a) of the Securities Exchange Act 1934, as amended ("Exchange Act"),
against all loss, claim, damage, expense or liability (including all reasonable
attorneys' fees and other expenses reasonably incurred in investigating,
preparing, or defending against any claim whatsoever incurred by the indemnified
party in any action or proceeding between the indemnitor and indemnified party
or between the indemnified party and any third party or otherwise) to which any
of them may become subject under the Securities Act, the Exchange Act or any
other statute or at common law or otherwise under laws of foreign countries,
arising from such registration statement or based upon any untrue statement or
alleged untrue statement of a material fact contained in (i) any preliminary
prospectus, registration statement or prospectus (as from time to time each may
be amended and supplemented); (ii) in any post-effective amendment or amendments
or any new registration statement and prospectus in which is included the
Registrable Securities; or (iii) any application or other document or written
communication (collectively called "application") executed by the Company or
based upon written information furnished by the Company in any jurisdiction in
order to qualify the Registrable Securities under the securities laws thereof or
filed with the commission, any state securities commission or agency, Nasdaq or
any securities exchange; or the omission or alleged omission therefrom of a
material fact required to be stated therein or necessary to make the statements
therein, in light of the circumstances under which they were made, not
misleading; unless such statement or omission is made in reliance upon, and in
strict conformity with, written information furnished to the Company with
respect to the holders expressly for the use in a preliminary prospectus,
registration statement or prospectus, or any amendment supplement thereof, or in
any application, as the case may be. The Company agrees promptly to notify the
Warrantholder of the commencement of any litigation proceedings against the
Company or any of its officers, directors or controlling persons in connection
with the issue and sale or resale of the Shares or in connection with any such
registration statement or prospectus.

         12. Fractional Shares

         Upon exercise of the Warrants the Company shall not be required to
issue fractional shares of Common Stock or other capital stock. In lieu of such
fractional shares, the Warrantholder shall receive an amount in cash equal to
the same fraction of the (i) current Market Price of one whole Share if clause
(i), (ii) or (iii) in the definition of Market Price in Section 2 above is
applicable or (ii) book value of one whole Share as reported in the Company's
most recent audited financial statements if clause (iv) in the definition of
Market Price in Section 2 above is applicable. All calculations under this
Section 12 shall be made to the nearest cent.

<PAGE>

         13. Securities Act Legend

         The Warrantholder shall not be entitled to any rights of a stockholder
of the Company with respect to any Shares purchasable upon the exercise hereof,
including voting, dividend or dissolution rights, until such Shares have been
paid for in full. As soon as practicable after such exercise, the Company shall
deliver a certificate or certificates for the securities issuable upon such
exercise, all of which shall be fully paid and nonassessable, to the person or
persons entitled to receive the same; provided, however, that, if applicable,
such certificate or certificates delivered to the holder of the surrendered
Warrant shall bear a legend reading substantially as follows:

         "These securities have not been registered under the Securities Act of
         1933, as amended, or the securities laws of any state and may not be
         sold or transferred in the absence of such registration or any
         exemption therefrom under such Act and laws, if applicable. The
         Company, prior to permitting a transfer of these securities, may
         require an opinion of counsel or other assurances satisfactory to it as
         to compliance with or exemption from such Act and laws."

         14. Notice of Adjustment

         (a) Upon any adjustment of the Purchase Price pursuant to Section 10
above, the Company, within 30 calendar days thereafter, shall have on file for
inspection by the Warrantholder a certificate of the Board of Directors of the
Company setting forth the Purchase Price after such adjustment, the method of
calculation thereof in reasonable detail, the facts upon which such calculations
were based and the number of Shares issuable upon exercise of a Warrant after
such adjustment in the Purchase Price, which certificate shall be conclusive
evidence of the correctness of the matters set forth therein.

         (b) In case:

             (i) the Company shall authorize the issuance to all holders of
Common Stock of rights, options or warrants to subscribe for or purchase capital
stock of the Company or of any other subscription rights, options or warrants;
or

             (ii) the Company shall authorize the distribution to all holders of
Common Stock of evidences of its indebtedness or assets; or

             (iii) of any consolidation or merger to which the Company is a
party and for which approval of any stockholders of the Company is required, of
the conveyance or transfer of the properties and assets of the Company
substantially as an entirety or of any capital reorganization or any
reclassification of the Common Stock (other than a change in par value or from a
specified par value to no par value or from no par value to a specified par
value or as a result of a subdivision or combination); or

<PAGE>

             (iv) of the voluntary or involuntary dissolution, liquidation or
winding up of the Company; or

             (v) the Company proposes to take any other action which would
require an adjustment of the Purchase Price pursuant to Section 10 above;

then, in each such case, the Company shall give to the Warrantholder at its
address appearing below at least 20 calendar days prior to the applicable record
date hereinafter specified in (A), (B), or (C) below, by first class mail,
postage prepaid, a written notice stating (A) the date as of which the holders
of record of shares of Common Stock entitled to receive any such rights,
options, warrants or distribution are to be determined or (B) the date on which
any such consolidation, merger, conveyance, transfer, reorganization,
reclassification, dissolution, liquidation or winding up is expected to become
effective, and the date as of which it is expected that holders of record of
shares of Common Stock shall be entitled to exchange such shares for securities
or other property, if any, deliverable upon such consolidation, merger,
conveyance, transfer, reorganization, reclassification, dissolution, liquidation
or winding up or (C) the date of such action which would require an adjustment
of the Purchase Price. The failure to give the notice required by this Section
14(b) or any defect therein shall not affect the legality or validity of any
such issuance, distribution, consolidation, merger, conveyance, transfer,
reorganization, reclassification, dissolution, liquidation, winding up or other
action or the vote upon any such action.

         Except as provided herein, nothing contained herein shall be construed
as conferring upon the Warrantholder the right to vote on any matter submitted
to the stockholders of the Company for their vote or to receive notice of
meetings of stockholders or the election of directors of the Company or any
other proceedings of the Company, or any rights whatsoever as a stockholder of
the Company.

         15. Notices

         Any notice, request, demand or other communication pursuant to the
terms of the Warrants shall be in writing and shall be sufficiently given or
made when delivered or mailed by first class or registered mail,
postage-prepaid, to the following addresses:

<PAGE>

         If to the Company:

                 Network-1 Security Solutions, Inc.
                 1601 Trapelo Road
                 Reservoir Place
                 Waltham, Massachusetts 02451
                 Attn: Avi A. Fogel, President and Chief Executive Officer

         with a copy to:

                 Solovay Edlin & Eiseman, P.C.
                 845 Third Avenue, 8th Floor
                 New York, New York 10022
                 Attention:  Sam Schwartz, Esq.

         If to the Warrantholder, to the address of such Warrantholder provided
to the Company by such Warrantholder for the purpose of notices, or to such
other address or such other counsel as the Company or the Warrantholder may
designate by written notice to the other party.

         16. Miscellaneous

         (a) All the covenants and provisions herein by or for the benefit of
the Company shall bind and inure to the benefit of its successors or assigns and
all of the covenants and provisions herein for the benefit of the Warrantholder
hereof shall inure to the benefit of its successors or assigns.

         (b) This warrant certificate shall be deemed to be a contract made
under the laws of the State of New York for all purposes and shall be construed
in accordance with the laws of such State.

         (c) Nothing in this warrant certificate shall be construed to give any
person or corporation other than the Company and the Warrantholder and its
permitted transferees any legal or equitable right, remedy or claim under this
warrant certificate; but this warrant certificate shall be for the sole and
exclusive benefit of the Company and the Warrantholder and its permitted
transferees.

<PAGE>

         IN WITNESS WHEREOF, an authorized office of the Company has
signed and delivered to the Warrantholder this warrant certificate as of the
date first written above.

                 NETWORK-1 SECURITY SOLUTIONS, INC.

                 By:___________________________________________
                                         Avi A. Fogel,
                      President and Chief Executive Officer

ATTEST:

By:      __________________________________
         Murray P. Fish,
         Chief Financial Officer and Secretary

[CORPORATE SEAL]

<PAGE>

                              ELECTION TO PURCHASE

(To be executed by the registered holder if such holder desires to exercise the
within Warrants)

         To:      Network-1 Security Solutions, Inc.
                  1601 Trapelo Road
                  Reservoir Place
                  Waltham, MA 02451
                  Attn: Murray P. Fish, Chief Financial Officer and Secretary

The undersigned hereby (1) irrevocably elects to exercise his or its rights to
purchase _____ shares of Common Stock covered by the within Warrants, (2) makes
payment in full of he Purchase Price by enclosure of a certified check, (3)
requests that certificates for such shares be issued in the name of:

Please print name, address and Social Security or Tax Identification Number:

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and (4) if said number of shares shall not be all the shares evidenced by the
within Warrants, requests that a new warrant certificate for the balance of the
shares covered by the within Warrants be registered in the name of, and
delivered to:

Please print name and address:

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

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                  In lieu of receipt of a fractional share of Common Stock, the
undersigned will receive a check representing payment therefor.

Dated:  _____________________            _________________________________

                      By:_________________________________

                         _________________________________<PAGE>

                                                                     Exhibit 4.3

                               PENTON MEDIA, INC.
                         MANAGEMENT STOCK PURCHASE PLAN
           (As Amended and Restated Effective as of January 1, 2000)

                                   ARTICLE I

                              Purpose of the Plan

     The purpose of the Penton Media, Inc. Management Stock Purchase Plan (As
Amended and Restated Effective as of January 1, 2000) (the "Plan") is to provide
a means for designated officers and other key employees of Penton Media, Inc.
(the "Company") and its Subsidiaries to acquire a proprietary interest (or
increase an existing interest) in the Company.  Participants in the Plan may
elect to receive restricted stock units ("RSUs") in lieu of a designated portion
of up to one hundred percent (100%) of their annual incentive bonus ("Bonus")
under the Penton Media, Inc. Senior Executive Bonus Plan or other similar
arrangement (the "Bonus Plan").  Each RSU represents the right to receive one
share of the common stock, par value $.01 of the Company (the "Common Stock")
upon the terms and conditions stated herein.  RSUs are granted at a discount of
20% of the Fair Market Value (as defined in Section 4.2 of the Plan) on the date
the RSUs are awarded.  So long as the participant remains employed by Company
for at least two years after the date of grant or until the occurrence of
certain specified events, his or her RSUs will be settled in shares of Common
Stock after a period of deferral selected by the participant, or upon
termination of employment, if earlier.

                                   ARTICLE II

                                 Administration

     The Plan shall be administered by the Compensation Committee (the
"Committee") of the Board of Directors of the Company (the "Board").  The
Committee shall have complete discretion and authority with respect to the Plan
and its application, except as expressly limited herein.  Determinations by the
Committee shall be final and binding on all parties with respect to all matters
relating to the Plan.

                                  ARTICLE III

                                  Eligibility

     Officers and other key employees of the Company and its Subsidiaries as
designated by the Committee shall be eligible to participate in the Plan.  For
all purposes of the Plan, the term "Subsidiary" means any corporation or other
legal entity in which the Company owns, directly or indirectly, an equity
interest.

                                   ARTICLE IV

                                 Participation

     4.1  Generally.  Participation in the Plan shall be based on the award of
RSUs.  Each RSU awarded to a participant shall be credited to a bookkeeping
account established and maintained for that participant.

     4.2  Price of RSUs.  The "Price" of each RSU shall be equal to eighty
percent (80%) of the Fair Market Value on the date the RSU is awarded.  For all
purposes of the Plan, the "Fair Market Value" on any given date shall mean the
average of the high and low sales price of a share of Common Stock on the New
York Stock Exchange or other public exchange on which the Common Stock is traded
on such date or, if the Common Stock is not publicly traded on such date, the
value of the Common Stock as determined by the Committee.
<PAGE>

     4.3  Election to Participate.  No later than March 31 of any year, each
participant may elect to receive RSUs in lieu of all or a specified part of his
or her Bonus that may become payable to him or her for performance in such year
under the Bonus Plan that in the absence of such election would be payable in
the following year; provided, however, that, with respect to any Bonus payable
in 2000, a participant may make an election on or prior to September 10, 1999.
Such election shall be made on an election form specified by the Committee (an
"Election Form") and filed with the Committee. An Election Form that is timely
delivered shall be effective for the Bonus earned in the relevant calendar year
(or, with respect to any Bonus payable in 2000, earned in 1999).  Such election
may be expressed as a specified percentage (up to one hundred percent (100%)) of
the participant's actual Bonus amount or a specified dollar amount (up to one
hundred percent (100%)) of the participant's Bonus.  Any percentage amount
specified must be at least 10% of the Bonus otherwise payable.  Any dollar
amount specified must be at least $5,000.  Amounts specified are entirely
contingent on the amount of Bonus actually awarded.

     4.4  Deferral Period.  Each Election Form shall specify a deferral period
for the RSUs to which it pertains (the "Deferral Period").  The Deferral Period
shall be expressed as a number of whole years, not less than two, beginning on
the award date.  Subject to the approval of the Company as described below in
this Section, a participant may make a subsequent election requesting a change
in the Deferral Period (subject to the limitations set forth in this Section).
Such subsequent election shall be on a form provided by the Company, which form
must be filed with the Company (a) at a time at which the participant is an
employee of the Company or a Subsidiary and (b), except as described below in
the sentence that immediately follows, at least one (1) year prior to the date
on which the participant otherwise would be entitled to receive shares of Common
Stock.  The one (1) year notice requirement described above, however, does not
apply in the case where the participant otherwise would be entitled to receive
shares of Common Stock following an involuntary termination of the participant's
employment, including by reason of death or permanent disability.

     4.5  Awards.  Once each year, on the date that Bonuses are paid or would
otherwise be paid, the Company shall award RSUs to each participant as follows:
Each participant's account shall be credited with a whole number of RSUs
determined by dividing the amount (expressed in dollars) that is determined
under his or her Election Form by the Price of each RSU awarded on such date.
No fractional RSU will be credited and the amount equivalent in value to the
fractional RSU will be paid out to the participant currently in cash.

                                   ARTICLE V

                             Vesting and Settlement

     5.1  Normal Vesting.  A participant shall be fully vested in each RSU on
the second anniversary of the date of award of the RSU.

     5.2  Accelerated Vesting.  Notwithstanding Section 5.1 of the Plan, a
participant's RSUs shall immediately become completely vested upon the
participant's death or permanent disability or upon a Change of Control (as
defined in Section 5.5 of the Plan).

     5.3  Settlement After Vesting.  With respect to each vested RSU, the
Company shall issue to the participant one share of Common Stock as soon as
practicable after the end of the Deferral Period specified in the participant's
Election Form pertaining to such RSU, or, if earlier, (a) upon the participant's
termination of employment in accordance with the provisions of Section 5.4 of
the Plan, or (b) the termination of the Plan.

     5.4  Settlement Prior to Vesting.

          (a) If a participant voluntarily terminates his or her employment with
     the Company, or the participant is terminated for Cause (as defined in
     Subsection 5.4(d) of the Plan), the participant's nonvested RSUs shall be
     canceled and he or she shall receive a cash payment equal to the lesser of
     (i) the Price of such RSUs or (ii) an amount equal to the number of such
     RSUs multiplied by the Fair Market Value on the date of the participant's
     termination of employment.

          (b) If a participant's employment is terminated by the Company for any
     reason other than Cause, the participant's nonvested RSUs shall be canceled
     and he or she shall receive payment as follows:  The number of nonvested
     RSUs awarded with respect to each award date shall be multiplied by a
     fraction that is equal to the
<PAGE>

     number of full months that the participant was employed by the Company
     after each such award date divided by twenty-four (24) and the participant
     shall receive the resulting number of such RSUs in shares of Common Stock
     (with any fractional shares resulting from such calculation being settled
     in cash). With respect to the participant's remaining nonvested RSUs, the
     participant shall receive cash in an amount equal to the lesser of (a) the
     Price of such RSUs or (b) an amount equal to the number of such RSUs
     multiplied by the Fair Market Value on the date of the participant's
     termination of employment.

          (c)  The Committee shall have complete discretion to determine the
     circumstances of a participant's termination of employment, including
     whether the same results from voluntary termination, permanent disability,
     termination for Cause, or termination by the Company for any reason other
     than Cause.  The Committee's determination shall be final and binding on
     all parties and not subject to review or challenge by any participant or
     other person.

          (d)  For purposes of the Plan, "Cause" shall mean:

               (i)    the commission by the participant of a felony or a crime
                      involving moral turpitude;

               (ii)   the commission by the participant of a fraud;

               (iii)  the commission by the participant of any act involving
                      dishonesty or disloyalty with respect to the Company or
                      any of its Subsidiaries or affiliates that harms or
                      damages any of them to any extent;

               (iv)   conduct by the participant that brings the Company or
                      any of its Subsidiaries or affiliates into substantial
                      public disgrace or disrepute; or

               (v)    gross negligence or willful misconduct by the participant
                      with respect to the Company or any of its Subsidiaries
                      or affiliates.

     5.5  Change of Control.  For purposes of the Plan, "Change of Control"
shall mean the occurrence of any of the following events:

          (a)  The acquisition by any individual, entity or group (within the
     meaning of Section 13(d)(3) or 14(d)(2) of the Securities Exchange Act of
     1934, as amended (the "Exchange Act")) (a "Person") of beneficial ownership
     (within the meaning of Rule 13d-3 promulgated under the Exchange Act) of
     40% or more of  either: (i) the then-outstanding shares of Common Stock or
     (ii) the combined voting power of the then-outstanding voting securities of
     the Company entitled to vote generally in the election of directors
     ("Voting Stock"); provided, however, that for purposes of this Subsection
                       --------- -------
     5.4(a), the following acquisitions shall not constitute a Change of
     Control: (A) any acquisition directly from the Company, (B) any acquisition
     by the Company, a Subsidiary or the Harris Group (as defined in Section 5.6
     of the Plan), (C) any acquisition by any employee benefit plan (or related
     trust) sponsored or maintained by the Company or any Subsidiary, or (D) any
     acquisition by any Person pursuant to a transaction which complies with
     clauses (i), (ii) and (iii) of Subsection 5.5(c); or

          (b)  Individuals who, as of the date hereof, constitute the Board (the
     "Incumbent Board") cease for any reason (other than death or permanent
     disability) to constitute at least a majority of the Board; provided,
                                                                 ---------
     however, that any individual becoming a director subsequent to the date
     -------
     hereof whose election, or nomination for election by the Company's
     shareholders, was approved by a vote of at least a majority of the
     directors then comprising the Incumbent Board (either by a specific vote or
     by approval of the proxy statement of the Company in which such person is
     named as a nominee for director, without objection to such nomination)
     shall be considered as though such individual were a member of the
     Incumbent Board, but excluding for this purpose, any such individual whose
     initial assumption of office occurs as a result of an actual or threatened
     election contest (within the meaning of Rule 14a-11 of the Exchange Act)
     with respect to the election or removal of directors or other actual or
     threatened solicitation of proxies or consents by or on behalf of a Person
     other than the Board; or

          (c)  Consummation of a reorganization, merger or consolidation or sale
     or other disposition of all or substantially all of the assets of the
     Company (a "Business Combination"), in each case, unless, following such
<PAGE>

     Business Combination, (i) all or substantially all of the individuals and
     entities who were the beneficial owners, respectively, of the Common Stock
     and Voting Stock immediately prior to such Business Combination
     beneficially own, directly or indirectly, more than a majority of,
     respectively, the then-outstanding shares of common stock and the combined
     voting power of the then-outstanding voting securities entitled to vote
     generally in the election of directors, as the case may be, of the entity
     resulting from such Business Combination (including, without limitation, an
     entity which as a result of such transaction owns the Company or all or
     substantially all of the Company's assets either directly or through one or
     more Subsidiaries) in substantially the same proportions relative to each
     other as their ownership, immediately prior to such Business Combination,
     of the Common Stock and Voting Stock of the Company, as the case may be,
     (ii) no Person (excluding any entity resulting from such Business
     Combination, the Harris Group or any employee benefit plan (or related
     trust) sponsored or maintained by the Company, a Subsidiary or such entity
     resulting from such Business Combination) beneficially owns, directly or
     indirectly, 40% or more of, respectively, the then-outstanding shares of
     common stock of the entity resulting from such Business Combination, or the
     combined voting power of the then-outstanding voting securities of such
     corporation, except to the extent that such ownership existed prior to the
     Business Combination and (iii) at least a majority of the members of the
     board of directors of the corporation resulting from such Business
     Combination were members of the Incumbent Board at the time of the
     execution of the initial agreement, or of the action of the Board providing
     for such Business Combination; or

          (d)  Approval by the shareholders of the Company of a complete
     liquidation or dissolution of the Company.

     5.6  Harris Group.  For purposes of Section 5.5 of the Plan, the "Harris
Group" shall mean Messrs. Irving B. Harris, Neison Harris, King Harris, William
W. Harris and June H. Barrows, and their respective spouses, descendants and
spouses of descendants, trustees of trusts established for the benefit of such
persons (acting in their capacity as trustees of such trusts), and executors of
estates of such persons (acting in their capacity as executors of such estates),
and each entity of which any of the foregoing owns (a) more than fifty percent
(50%) of the voting stock or other voting interests and (b) stock or other
interests representing more than fifty percent (50%) of the total value of the
stock or other interests of such entity.

                                   ARTICLE VI

                          Dividend Equivalent Amounts

     Whenever dividends (other than dividends payable only in shares of stock)
are paid with respect to Common Stock, each participant shall be paid an amount
in cash equal to the number of his or her vested RSUs multiplied by the dividend
value per share.  In addition, each participant's account shall be credited with
an amount equal to the number of such participant's nonvested RSUs multiplied by
the dividend value per share.  Amounts credited with respect to each nonvested
RSU shall be paid, without interest, on the earlier of the date the participant
becomes vested in such RSU, or when the participant receives payment for his or
her nonvested RSUs pursuant to Section 5.4 of the Plan.

                                  ARTICLE VII

                           Designation of Beneficiary

     Upon the death of a participant, his or her account shall be paid to the
beneficiary or beneficiaries designated by him or her.  If there is no
designated beneficiary, or no designated beneficiary surviving at a
participant's death, payment of a participant's account shall be made to his or
her estate.  Beneficiary designations shall be made in writing.  A participant
may designate a new beneficiary or beneficiaries at any time by notifying the
Committee.

                                  ARTICLE VIII

                        Shares Available Under the Plan

     The aggregate maximum number of shares of Common Stock reserved and
available for issuance under the Plan shall be 250,000 shares of Common Stock.
For purposes of this limitation, the shares of Common Stock underlying any RSUs
that are canceled shall be added back to the shares of Common Stock available
for issuance under the Plan.  Such shares may be shares of original issuance or
treasury shares or a combination of the foregoing.
<PAGE>

                                  ARTICLE IX

                                  Adjustments

     The Committee may make or provide for such adjustments in the numbers of
shares of Common Stock covered by outstanding RSUs granted hereunder, in the
Price of each RSU, and in the kind of shares covered thereby, as the Committee,
in its sole discretion, exercised in good faith, may determine is equitably
required to prevent dilution or enlargement of the rights of participants that
otherwise would result from (a) any stock dividend, stock split, combination of
shares, recapitalization or other change in the capital structure of the
Company, or (b) any merger, consolidation, spin-off, split-off, spin-out, split-
up, reorganization, partial or complete liquidation or other distribution of
assets, issuance of rights or warrants to purchase securities, or (c) any other
corporate transaction or event having an effect similar to any of the foregoing.
Moreover, in the event of any such transaction or event, the Committee, in its
discretion, may provide in substitution for any or all outstanding awards under
the Plan such alternative consideration as it, in good faith, may determine to
be equitable in the circumstances and may require in connection therewith the
surrender of all awards so replaced.  The Committee may also make or provide for
such adjustments in the numbers of shares specified in Article VIII of the Plan
as the Committee in its sole discretion, exercised in good faith, may determine
is appropriate to reflect any transaction or event described in this Article IX.

                                   ARTICLE X

                      Amendment or Termination of the Plan

     The Company reserves the right to amend or terminate the Plan at any time,
by action of its Board, provided that no such action shall adversely affect a
participant's rights under the Plan with respect to RSUs awarded before the date
of such action.

                                   ARTICLE XI

                            Miscellaneous Provisions

     11.1 Taxes.  To the extent that the Company is required to withhold
Federal, state or local taxes in connection with any component of a
participant's compensation in cash or shares of Common Stock, and the amounts
available to the Company for such withholding are insufficient, it shall be a
condition to the receipt of any shares of Common Stock that the participant make
arrangements satisfactory to the Company for the payment of the balance of such
taxes required to be withheld, which arrangement may include relinquishment of
the shares of Common Stock.  The Company and a participant may also make similar
arrangements with respect to payment of any other taxes derived from or related
to the payment of shares of Common Stock with the respect to which withholding
is not required.

     11.2 Hardship Distributions.  Prior to the time a participant's account
becomes payable, the Committee, in its sole discretion, may elect to distribute
all or a portion of any vested RSUs in the participant's account in the event
such participant requests a distribution on account of severe financial
hardship.  For purposes of this Plan, severe financial hardship shall be deemed
to exist in the event the Committee determines that a participant needs a
distribution to meet immediate and heavy financial needs resulting from a sudden
or unexpected illness or accident of the participant or a member of his or her
family, loss of the participant's property due to casualty, or other similar
extraordinary and unforeseeable circumstances arising as a result of events
beyond the control of the participant.  A  distribution based on financial
hardship shall not exceed the amount required to meet the immediate financial
need created by the hardship.

     11.3 Assignment.  No right or interest of any participant (or any person
claiming through or under such participant, other than the surviving spouse of
such participant after the participant is deceased) in any benefit or payment
herefrom shall be assignable or transferable in any manner or be subject to
alienation, anticipation, sale, pledge, encumbrance or other legal process or in
any manner be liable for or subject to the debts or liabilities of such
participant.  If any participant or any such person (other than the surviving
spouse of such participant after the participant is deceased) shall attempt to
or shall transfer, assign, alienate, anticipate, sell, pledge or otherwise
encumber his or her benefits hereunder or any part thereof, or if by reason of
his or her bankruptcy or other event happening at any time such benefits would
devolve upon anyone else or would not be enjoyed by him or her, then the
Committee, in its discretion, may terminate his or her interest in any such
benefit to the extent the Committee considers necessary or advisable to prevent
<PAGE>

or limit the effects of such occurrence.  Termination shall be effected by
filing a written "termination declaration" with the Committee records and making
reasonable efforts to deliver a copy to such participant or other person or his
or her legal representative.

     As long as any individual whose interests hereunder are subject to a
termination declaration is alive, any benefits affected by the termination shall
be retained by the Company and, in the Committee's sole and absolute judgment,
may be paid to or expended for the benefit of such individual, his or her
spouse, his or her children or any other person or persons in fact dependent
upon him or her in such a manner as the Committee shall deem proper.  Upon the
death of any individual, all benefits withheld from him or her and not paid to
others in accordance with the preceding sentence shall be distributed to such
individual's estate or to his or her creditors and if such individual shall have
descendants, including adopted children, then living, distribution shall be made
to such individual's then living descendants, including adopted children, per
stirpes.

     11.4 Unfunded and Unsecured.  The Plan shall at all times be entirely
unfunded, and no provision shall at any time be made with respect to segregating
assets of the Company (including Common Stock) for payment of any amounts or
issuance of any shares of Common Stock hereunder.  No participant or other
person shall have any interest in any particular assets of the Company
(including Common Stock) by reason of the right to receive payment under the
Plan, and any participant or other person shall have only the rights of a
general unsecured creditor of the Company with respect to any rights under the
Plan.

     11.5 Governing Law.  The terms of the Plan shall be governed construed,
administered and regulated in accordance with the laws of the State of Ohio.

     11.6 Effective Date.  The Plan shall become effective as of August 26,
1999.

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