<PAGE>   1
                                                                    EXHIBIT 10.3

                            STOCK PURCHASE AGREEMENT*

                                 BY AND BETWEEN


                     SECURITY FIRST TECHNOLOGIES CORPORATION

                                       AND

                         AC II TECHNOLOGY (ACT II) B.V.









                          DATED AS OF FEBRUARY 19, 1999




* AS AMENDED ON APRIL 30, 1999


<PAGE>   2



                                TABLE OF CONTENTS

<TABLE>
<CAPTION>
                                                                                           Page
                                                                                           ----

<S>                                                                                          <C>
SECTION 1.  PURCHASE AND SALE OF THE SHARES..............................................     1
            -------------------------------
      1.1  Sale and Issuance of the Shares...............................................     1
           -------------------------------
      1.2  Closing.......................................................................     2
           -------
SECTION 2.  REGISTRATION OF THE SHARES...................................................     2
            --------------------------
SECTION 3.  REPRESENTATIONS AND WARRANTIES OF THE CORPORATION............................     6
            -------------------------------------------------
      3.1  Organization and Standing.....................................................     6
           -------------------------
      3.2  Authorization; Binding Obligation.............................................     6
           ---------------------------------
      3.3  Capitalization................................................................     6
           --------------
      3.4  Validity of Shares; Issuance..................................................     7
           ----------------------------
      3.5  No Consents...................................................................     7
           -----------
      3.6  Non-Contravention.............................................................     7
           -----------------
      3.7  Additional Information........................................................     7
           ----------------------
SECTION 4.  REPRESENTATIONS AND WARRANTIES OF
            ---------------------------------
      PURCHASER..........................................................................     8
      ---------
      4.1  Organization and Standing.....................................................     8
           -------------------------
      4.2  Authorization.................................................................     8
           -------------
      4.3  Non-Contravention.............................................................     8
           -----------------
      4.4  No Consents...................................................................     9
           -----------
      4.5  Adequate Resources............................................................     9
           ------------------
      4.6  Investment Experience.........................................................     9
           ---------------------
      4.7  Investment Intent.............................................................     9
           -----------------
      4.8  Registration or Exemption Requirements........................................    10
           --------------------------------------
      4.9  No Legal, Tax or Investment Advice............................................    10
           ----------------------------------
SECTION 5.  ADDITIONAL AGREEMENTS........................................................    10
            ---------------------
      5.1  Permitted Transfers...........................................................    10
           -------------------
      5.2  Other Approvals...............................................................    10
           ---------------
SECTION 6.  CONDITIONS TO CLOSING........................................................    11
            ---------------------
      6.1  Conditions to Obligations of All Parties......................................    11
           ----------------------------------------
      6.2  Conditions to Obligations of Purchaser........................................    11
           --------------------------------------
      6.3  Conditions to Obligations of the Corporation..................................    12
           --------------------------------------------
SECTION 7.  CLOSING......................................................................    12
            -------
      7.1  Deliveries by the Corporation.................................................    12
           -----------------------------
      7.2  Deliveries by the Purchaser...................................................    12
           ---------------------------
SECTION 8.  LEGEND.......................................................................    13
            ------
      8.1  Endorsement...................................................................    13
           -----------
      8.2  Removal of Legend.............................................................    13
           -----------------
SECTION 9.  TERMINATION..................................................................    13
            -----------
      9.1  Mutual Consent................................................................    13
           --------------
      9.2  Other Termination.............................................................    14
           -----------------
</TABLE>


<PAGE>   3

<TABLE>
<S>                                                                                          <C>
      9.3  Effect of Termination.........................................................    14
           ---------------------
SECTION 10.  MISCELLANEOUS...............................................................    14
             -------------
      10.1  Additional Actions and Documents.............................................    14
            --------------------------------
      10.2  Expenses.....................................................................    15
            --------
      10.3  Notices......................................................................    15
            -------
      10.4  Waiver.......................................................................    16
            ------
      10.5  Binding Effect...............................................................    16
            --------------
      10.6  Entire Agreement; Amendment..................................................    16
            ---------------------------
      10.7  Severability.................................................................    16
            ------------
      10.8  Headings.....................................................................    16
            --------
      10.9  Governing Law................................................................    17
            -------------
      10.10  Signature in Counterparts...................................................    17
             -------------------------
      10.11  No Third Party Beneficiaries................................................    17
             ----------------------------
      10.12  Assignability...............................................................    17
             -------------
      10.13  Parties Not Partners........................................................    17
             --------------------
</TABLE>
<PAGE>   4

                            STOCK PURCHASE AGREEMENT

          This Stock Purchase Agreement ("Agreement"), dated as of the 19th day 
of February, 1999, is entered into by and among Security First Technologies
Corporation, a Delaware corporation (the "Corporation") and AC II Technology
(ACT II) B.V., a private limited company organized under the laws of the
Netherlands ("Purchaser").

          WHEREAS, Purchaser desires to subscribe for, and acquire from the
Corporation, a number of shares (the "Shares") of the Corporation's common
stock, par value $.01 per share ("Common Stock"), as determined by dividing the
Purchase Price (as defined below in Section 1.1(a)) by the applicable per share
price of the Shares (as described below in Section 1.1), on the terms and under
the conditions specified herein;

          WHEREAS, the Corporation desires to sell and issue to Purchaser the 
Shares on the terms and under the conditions specified herein; and

          *

          NOW, THEREFORE, in consideration of the mutual promises, 
representations, warranties, covenants and conditions set forth in this 
Agreement, the sufficiency of which is hereby acknowledged, the parties mutually
agree as follows:

SECTION 1.  PURCHASE AND SALE OF THE SHARES.

     1.1  Sale and Issuance of the Shares.

          1.1.     At the Closing (as defined below in Section 1.2(a)) and
subject to the terms and conditions of this Agreement, Purchaser hereby
subscribes for, and agrees to purchase, the Shares, and the Corporation agrees
to sell and issue to Purchaser at the Closing for the Purchase Price, the
Shares. The aggregate purchase price to be paid by Purchaser shall be $4,000,000
(such aggregate amount, the "Purchase Price"), and the number of Shares shall be
determined by dividing the Purchase Price by the average closing asking price
per share of the Common Stock, as quoted on the Nasdaq Stock Market National
Market Tier, for each of the 10 trading days preceding the business day
immediately before the Closing Date (as defined in Section 1.2(a) below), and
rounding down to the nearest whole share, if the quotient would otherwise
produce fractional shares. The number of Shares shall then be doubled so as to
give effect to the Split as if the Split had been paid immediately prior to the
Closing.

*  Recital deleted.
<PAGE>   5

     1.2  Closing.

          1.2(a).  The closing (the "Closing") of the transaction shall take
place on April 30, 1999, or such other date not later than May 15, 1999 as the
parties hereto shall mutually agree (the "Closing Date"). 

          1.2(b).  The Closing shall take place on the Closing Date at 10:00
a.m., Washington, D.C. time, at the offices of Hogan & Hartson L.L.P., 555 13th
Street, N.W., Washington, D.C. 20004, or at such other time and place as the
parties shall mutually agree.

SECTION 2.  REGISTRATION OF THE SHARES.

          2.1(a).  The Corporation shall within 180 days of the Closing Date
(unless Purchaser in its sole discretion agrees to extend such time period, in
which case the Corporation shall file as soon as reasonably practicable) a
registration statement ("Registration Statement") with the SEC to effect the
registration under the Securities Act of the Shares eligible for sale by
Purchaser in accordance with the following:

               (i)  The Corporation shall not be required to conduct an
     underwritten offering.

               (ii)  If, after it becomes effective, such Registration Statement
     is interfered with by any stop order, injunction or other order or
     requirement of the SEC (or any successor regulator thereto as to federal
     securities laws) or any other governmental authority, such registration
     shall not be deemed to have been effected unless such stop order,
     injunction or other order shall have been subsequently vacated or removed.

               (iii)  The Corporation shall have no obligation to include the
     Shares owned by Purchaser in a Registration Statement unless and until
     Purchaser has furnished the Corporation with all information and statements
     about or pertaining to Purchaser in such reasonable detail and on such
     timely basis as is reasonably deemed by the Corporation to be necessary or
     appropriate for the preparation of the Registration Statement.

               (iv)  The Corporation shall, subject to the other provisions of
     this Section 2:

                    (1)  use its reasonable efforts to cause the Registration
          Statement to become effective as soon as practicable after the filing
          thereof;

                    (2)  prepare and file with the SEC as promptly as is
          reasonably practicable such amendments and supplements to the
          Registration Statement contained therein as may be necessary to keep
          such Registration Statement effective until the first anniversary of
          the Closing Date or until Purchaser has completed the distribution
          described in such Registration Statement, whichever occurs first;

<PAGE>   6
                    (3)  furnish to Purchaser the number of copies of such
          Registration Statement, each amendment and supplement thereto;

                    (4)  use reasonable efforts to register or qualify such
          shares under the state blue sky or securities or banking laws ("Blue
          Sky Laws") of such jurisdictions as Purchaser reasonably requests (and
          to keep such registrations and qualifications effective for a period
          of three months, or until Purchaser has completed the distribution of
          such shares, whichever occurs first), and to do any and all other acts
          and things that may be reasonably necessary or advisable to enable
          such Purchaser to consummate the disposition of such shares in such
          jurisdictions; provided, however, that the Corporation will not be
          required to do any of the following: (i) qualify generally to do
          business in any jurisdiction where it would not be required but for
          this Section 2, (ii) subject itself to taxation in any such
          jurisdiction, or (iii) file any general consent to service of process
          in any such jurisdiction;

                    (5)  promptly notify Purchaser at any time during the period
          that the Corporation is required to keep the Registration Statement
          effective, of the occurrence of any event as a result of which such
          Registration Statement contains an untrue statement of a material fact
          or omits any fact necessary to make the statements therein in the
          light of the circumstances under which they were made, not misleading,
          and prepare a supplement or amendment to the Registration Statement so
          that, as thereafter delivered to the purchasers of such shares, the
          Registration Statement will not contain an untrue statement of a
          material fact or omit to state any fact necessary to make the
          statements therein, in the light of the circumstances under which they
          were made, not misleading; and

                    (6)  use reasonable efforts to cause all such shares to be
          listed on a securities exchange or the Nasdaq National Market System.

               (v)  If, pursuant to this Section 2, the Shares owned by 
     Purchaser are included in a Registration Statement, then Purchaser shall 
     pay all transfer taxes, if any, relating to the sale of the Shares, the 
     fees and expenses of its own counsel, and its pro rata portion of any 
     underwriting discounts or commissions or the equivalent thereof.

               (vi)  Except for the fees and expenses specified in paragraph (v)
     of this Section 2 and except as provided this paragraph (vi), the
     Corporation shall pay all expenses incident to the registration and to the
     Corporation's performance of or compliance with this Agreement, including,
     without limitation, all registration and filing fees, fees and expenses of
     compliance, with Blue Sky Laws, underwriting discounts, fees, and expenses
     (other than Purchaser's pro rata portion of any underwriting discounts or
     commissions or the equivalent thereof), printing expenses, messenger and
     delivery expenses, and fees and expenses of counsel for the Corporation and
     all independent certified public accountants and other persons retained by
     the Corporation.

               (vii)  In the event that the Shares owned by Purchaser are sold 
     by means of a Registration Statement pursuant to this Section 2, Purchaser
     (for the purposes of this paragraph (vii), the "Indemnifying Person")
     agrees to indemnify and hold harmless the Corporation, each of the
     Corporation's officers and directors, and each person, if any, who controls
     or may control the Corporation within the meaning of the Securities Act
     (for the purposes of this paragraph (vii), the Corporation, its officers
     and directors, and any such other persons being referred to individually as
     an "Indemnified Person" and collectively as "Indemnified Persons") from and
     against all demands, claims, actions or causes of action, assessments,
     losses, damages, liabilities, costs, and expenses, including, without
     limitation,

<PAGE>   7
interest, penalties, and reasonable attorneys' fees and disbursements, asserted
against, resulting to, imposed upon, or incurred by such Indemnified Person,
directly or indirectly (collectively, referred to for purposes of this paragraph
(vii) and the corresponding provision of paragraph (viii) below in the singular
as a "Claim" and in the plural as "Claims"), based upon, arising out of, or
resulting from any untrue statement of a material fact contained in the
Registration Statement or any omission to state therein a material fact
necessary in order to make the statements made therein, in the light of the
circumstances under which they were made, not misleading, to the extent that
such Claim is based upon, arises out of or results from any untrue statement or
omission based upon information furnished to the Corporation by Purchaser in a
written document provided by Purchaser for use in connection with the
Registration Statement.

              (viii)  The Corporation (for the purposes of this paragraph
(viii), the "Indemnifying Person") agrees to indemnify and hold harmless
Purchaser and any underwriters participating in the distribution of Common Stock
pursuant to a Registration Statement (for the purposes of this paragraph (viii),
Purchaser and any such other persons also being referred to individually as an
"Indemnified Person" and collectively as "Indemnified Persons") from and against
all Claims based upon, arising out of, or resulting from any untrue statement of
a material fact contained in the Registration Statement or any omission to state
therein a material fact necessary in order to make the statement made therein,
in the light of the circumstances under which they were made, not misleading,
provided that the Corporation will not be liable in any such case to the extent
that any such Claim arises out of or results from any untrue statement or
omission based upon information furnished to the Corporation by Purchaser in a
written document provided by Purchaser for use in connection with the
Registration Statement.

               (ix)   The indemnification set forth herein shall be in addition
to any liability the Corporation or Purchaser may otherwise have in connection
with any registration of the Shares. Within a reasonable time after receiving
definitive notice of any Claim in respect of which an Indemnified Person may
seek indemnification under this Section 2, such Indemnified Person shall submit
written notice thereof to such Indemnifying Person. The failure of the
Indemnified Person so to notify the Indemnifying Person of any such Claim shall
not relieve the Indemnifying Person from any liability it may have hereunder
except to the extent that (a) such liability was caused or increased by such
omission, or (b) the ability of the Indemnifying Person to reduce such liability
was materially adversely affected by such omission. In addition, the omission of
the Indemnified Person so to notify the Indemnifying Person of any such Claim
shall not relieve the Indemnifying Person from any liability it may have
otherwise than hereunder. The Indemnifying Person shall have the right to
undertake, by counsel or representatives of its own choosing, the defense,
compromise, or settlement (without admitting liability of the Indemnifying
Person) of any such Claim asserted, such defense, compromise, or settlement to
be undertaken at the expense and risk of the Indemnifying Person, and the
Indemnified Person shall have the right to engage separate counsel, at its own
expense, which counsel for the Indemnifying Person shall keep informed and
consult with in a reasonable manner. In the event the Indemnifying Person shall
fail to undertake such defense by its own representatives, the Indemnifying
Person shall give prompt written notice of such election to the Indemnified
Person, and the Indemnified Person shall undertake the defense, compromise, or
settlement (without admitting liability of the Indemnified Person) thereof on
behalf of and for the account and risk of the Indemnifying Person by counsel or
other representatives designated by the Indemnified Person. In the event that
any Claim shall arise out of a transaction or cover any period or periods
wherein the Corporation and Purchaser shall each be liable hereunder for part of
the liability or obligation arising therefrom, then the parties shall, each
choosing its own counsel and bearing its own expenses, defend such Claim, and no
settlement or compromise of such Claim may be made without the joint consent or
approval of the

<PAGE>   8
     Corporation and Purchaser. Notwithstanding the foregoing, no Indemnifying
     Person shall be obligated hereunder with respect to amounts paid in
     settlement of any Claim if such settlement is effected without the consent
     of such Indemnifying Person (which consent shall not be unreasonably
     withheld).

               (x)  If the indemnification provided for in this Section 2 is 
     held by a court of competent jurisdiction to be unavailable to an
     Indemnified Party (as defined in either paragraph (vii) or (viii)) with
     respect to any Claim, then Purchaser or the Corporation, as applicable and
     as the case may be (each an "Indemnifying Party"), in lieu of indemnifying
     an Indemnified Party hereunder, shall contribute to the amount paid or
     payable by such Indemnified Party as a result of such Claim in such
     proportion as is appropriate to reflect the relative fault of the
     Indemnifying Party on the one hand and of the Indemnified Party on the
     other in connection with the statements or omissions which resulted in such
     claim.

SECTION 3.  REPRESENTATIONS AND WARRANTIES OF THE CORPORATION.

          The Corporation represents and warrants to Purchaser as follows:

     3.1  Organization and Standing.

          The Corporation is a corporation duly incorporated, validly existing
and in good standing under the laws of the State of Delaware, and has the full
corporate power and authority to own and operate its properties and assets and
to carry on its business as currently conducted. The Corporation holds all
licenses and permits required for the conduct of its business as now conducted
which, if not in the Corporation's possession, could have a material adverse
effect on the Corporation's financial condition or results of operations, taken
as a whole. The Corporation is duly qualified as a foreign corporation and is in
good standing in all jurisdictions where the conduct of its business or its
ownership or leasing of property requires such qualification, except where the
failure to so qualify would not have a material adverse effect on the
Corporation's financial condition or results of operations, taken as a whole.

     3.2  Authorization; Binding Obligation.

          The Corporation has all requisite corporate power and authority to
enter into and to deliver this Agreement and perform its obligations hereunder.
The execution, delivery and performance of this Agreement by the Corporation and
the consummation of the transactions contemplated hereby have been duly
authorized by all necessary corporate action on the part of the Corporation.
This Agreement, when executed and delivered by the Corporation, shall constitute
a valid and binding obligation of the Corporation enforceable in accordance with
its terms, except as may be limited by applicable bankruptcy, insolvency,
reorganization, moratorium or other similar laws effecting the enforcement of
creditor's rights.

     3.3  Capitalization.

          The authorized capital stock of the Corporation consists of 60,000,000
shares of Common Stock, of which 12,263,502 are issued and outstanding as of
December 31, 1998, and 5,000,000 shares of preferred stock, of which 636,464 of
the 1,637,832 shares designated Series A Preferred Stock are issued and
outstanding as December 31, 1998 and of which all of the 749,064 Shares
designated Series B Redeemable Convertible Preferred Stock are issued and
outstanding as of December 31, 1998. All of the Corporation's outstanding shares
of capital stock were validly issued and are fully paid and nonassessable. As of
December 31, 1998, except for (i) 4,399,635 shares

<PAGE>   9
subject to issuance upon exercise of options and an additional 806,918 reserved
for issuance pursuant to options not yet granted, and (ii) shares reserved for
issuance upon conversion of the Series A Preferred Stock and the Series B
Preferred Stock, there are no shares of the Corporation's capital stock reserved
for issuance or any options, warrants, rights (including conversion or
preemptive rights) or agreements for the purchase from the Corporation of any
shares of its capital stock or securities exercisable for or convertible into
its capital stock.

     3.4  Validity of Shares; Issuance.

          The Shares, when issued in compliance with the provisions of this
Agreement will be validly issued, fully paid and nonassessable, and free of any
liens or encumbrances, and will be issued in compliance with all applicable
federal banking laws.

     3.5  No Consents.

          No governmental orders, permissions, consents, approvals or
authorizations are required to be obtained by the Corporation and no filings are
required to be made by the Corporation in connection with the execution and
delivery of this Agreement and the issuance of the Shares hereunder, except as
have been so obtained or made prior to the Closing or, with respect to any that
need to be obtained or made subsequent to the Closing, as will be obtained or
made in a timely manner after the Closing, except where the failure to obtain
such orders, permissions, consents, approvals or authorizations or to make such
filings would not have a material adverse effect on the Corporation's financial
condition or results of operations or business prospects, taken as a whole.

     3.6  Non-Contravention.

          The execution, delivery and performance of, and compliance with, this
Agreement will not (a) violate any provision of the articles of incorporation or
bylaws of the Corporation; (b) conflict with or result in a breach of, or
default under, or result in the creation of any lien, claim, charge or other
encumbrance upon any of the assets or properties of the Corporation pursuant to
the provisions of any material agreement, mortgage, indenture or other document
or instrument to which the Corporation is a party or by which the Corporation or
any of its properties or assets is bound, or (c) violate any existing statutes,
laws, ordinances, regulations, orders and other rules of law applicable to the
Corporation or any of its properties or assets, or applicable to the
Corporation's power or authority to perform its obligations under this
Agreement.

     3.7  Additional Information.

          The information contained in the Corporation's registration statement
on Form 8-A, as filed with the SEC on September 30, 1998, and all other reports
filed subsequent thereto through the date hereof pursuant to Section 13(a) or
15(d) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"),
did not at the respective dates of filing with the SEC contain any untrue
statement of a material fact or omit to state a material fact necessary in order
to make the statements therein, in light of the circumstances under which they
were made, not misleading.

SECTION 4.  REPRESENTATIONS AND WARRANTIES OF PURCHASER.

          Purchaser represents and warrants to the Corporation as follows:
<PAGE>   10
     4.1  Organization and Standing.

          Purchaser is a private limited company duly organized, validly
existing and in good standing under the laws of the Netherlands. Purchaser has
the full corporate power and authority to own and operate its properties and
assets and to carry on its business as currently conducted. Purchaser holds all
licenses and permits required for the conduct of its business as now conducted
which, if not in Purchaser's possession, could have a material adverse effect on
Purchaser's financial condition or results of operations, taken as a whole.
Purchaser is duly qualified and is in good standing in all jurisdictions where
the conduct of its business or its ownership or leasing of property requires
such qualification, except where the failure to so qualify would not have a
material adverse effect on Purchaser's financial condition or results of
operations, taken as a whole. Purchaser is a member of the Andersen Consulting
Worldwide Organization (as defined below) and is an affiliate of Andersen
Consulting LLP.

     4.2  Authorization.

          Purchaser has all requisite power and authority to enter into and to
deliver this Agreement. The execution, delivery and performance of this
Agreement by Purchaser and the consummation of the transactions contemplated
hereby have been duly authorized by all necessary action on the part of
Purchaser. This Agreement, when executed and delivered by Purchaser, shall
constitute a valid and binding obligation of Purchaser enforceable in accordance
with its terms, except as may be limited by applicable bankruptcy, insolvency,
reorganization, moratorium or other similar laws effecting the enforcement of
creditor's rights.

     4.3  Non-Contravention.

          The execution, delivery and performance of, and compliance with, this
Agreement will not (a) violate any provision of the governing instruments of
Purchaser; (b) conflict with or result in a breach of, or default under, or
result in the creation of any lien, claim, charge or other encumbrance upon any
of the assets or properties of Purchaser pursuant to the provisions of any
material agreement, mortgage, indenture or other document or instrument to which
Purchaser is a party or by which Purchaser or any of its properties or assets is
bound, or (c) violate any existing statutes, laws, ordinances, regulations,
orders and other rules of law applicable to Purchaser or any of its properties
or assets, or applicable to Purchaser's power or authority to perform its
obligations under this Agreement.

     4.4  No Consents.

          No governmental orders, permissions, consents, approvals or
authorizations are required to be obtained by Purchaser and no filings are
required to be made by Purchaser in connection with the execution and delivery
of this Agreement and the purchase of the Shares hereunder, except as have been
so obtained or made prior to the Closing or, with respect to any that need to be
obtained or made subsequent to the Closing, as will be obtained or made in a
timely manner after the Closing, except where the failure to obtain such orders,
permissions, consents, approvals or authorizations or to make such filings would
not have a material adverse effect on Purchaser's financial condition or results
of operations or business prospects, taken as a whole.

     4.5  Adequate Resources.

          Purchaser has sufficient cash and other resources to perform its
obligations hereunder.

<PAGE>   11
     4.6  Investment Experience.

          Purchaser is an  "accredited  investor"  as defined in Rule 501(a)
under the  Securities  Act.  Purchaser is aware of the Corporation's business
affairs and financial condition and has had access to and has acquired
sufficient information about the Corporation to reach an informed and
knowledgeable decision to acquire the Shares. Purchaser has such business and
financial experience as is required to give it the capacity to protect its own
interests in connection with the purchase of the Shares. Purchaser is able to
bear the economic risk of holding the Shares for an indefinite period, including
the loss of Purchaser's entire investment. The Shares were not offered or sold
to Purchaser by any form of general solicitation or advertising.

     4.7  Investment Intent.

          Purchaser is purchasing  the Shares for its own account as  principal,
for  investment  purposes  only,  and not with a view to, or for, resale,
distribution or fractionalization thereof, in whole or in part, within the
meaning of the Securities Act. Purchaser understands that its acquisition of the
Shares has not been registered under the Securities Act or registered or
qualified under any state securities law in reliance on specific exemptions
therefrom, which exemptions may depend upon, among other things, the bona fide
nature of Purchaser's investment intent as expressed herein.

     4.8  Registration or Exemption Requirements.

          Purchaser  further  acknowledges and understands that the Shares may
be required to be held  indefinitely,  and they may not be resold or otherwise
transferred except in a transaction registered under the Securities Act or where
an exemption from such registration is available. Purchaser understands that the
certificate(s) evidencing the Shares will be imprinted with a legend that
prohibits the transfer of the Shares unless (a) they are registered or such
registration is not required, and (b) if the transfer is pursuant to an
exemption from registration other than Rule 144 promulgated under the Securities
Act and, if the Corporation shall so request in writing, an opinion of counsel
satisfactory to the Corporation is obtained to the effect that the transaction
is so exempt and in compliance with applicable state law.

     4.9  No Legal, Tax or Investment Advice.

          Purchaser understands that nothing in this Agreement or any other
materials presented to Purchaser in connection with the purchase and sale of the
Shares constitutes legal, tax or investment advice. Purchaser has consulted such
legal, tax and investment advisors as it, in its sole discretion, has deemed
necessary or appropriate in connection with its purchase of the Shares.

Section 5.  ADDITIONAL AGREEMENTS.

     5.1  Permitted Transfers.

          For 180 days from the Closing Date, Purchaser may transfer some or all
of the Shares to a corporation,  partnership or other affiliate of Purchaser, if
such transferee agrees in writing to hold any Shares received subject to the
provisions of this Agreement and to transfer such Shares back to Purchaser if
such transferee ceases to be controlled by Purchaser. For purposes of this
section, an "affiliate of Purchaser" shall mean any member of the Andersen
Consulting Worldwide Organization or any entity which is at the relevant time
directly or indirectly controlled by any such entity or any entity which is
otherwise part of the Andersen Consulting Worldwide Organization. After the
above-referenced 180 day period, the restrictions of this section 5.1 shall no
longer apply.

<PAGE>   12
     5.2  Other Approvals.

          The parties shall cooperate and use their best efforts to obtain all
written consents and approvals of other persons in connection with the purchase
of the Shares contemplated hereby.

SECTION 6.  CONDITIONS TO CLOSING.

     6.1  Conditions to Obligations of All Parties.

          The obligations of each party to consummate the transactions
contemplated by this Agreement are subject to the satisfaction, on or before the
date of the Closing, of each of the following conditions precedent:

          6.1(a).  Termination. This Agreement shall not have been terminated in
accordance with its terms.

          6.1(b).  No Governmental Action. No action or proceeding by or before
any governmental authority shall have been instituted or threatened (and not
subsequently dismissed, settled or otherwise terminated) which is reasonably
expected to restrain, prohibit or invalidate the transactions contemplated by
this Agreement or to affect adversely the financial condition and business
prospects of the Corporation.

          6.1(c).  Third Party Consents. Receipt by the parties hereto of any
and all third party consents required by this Agreement.

     6.2  Conditions to the Obligations of Purchaser.

          The obligations of Purchaser to purchase the Shares contemplated by
this Agreement are subject to the satisfaction, on or before the date of the
Closing, of each of the following conditions precedent, any one or more of which
may be waived by Purchaser, in its sole and absolute discretion:

          6.2(a).  Representations and Warranties. The representations and
warranties of the Corporation contained in this Agreement shall be true, correct
and complete in all material respects when made and shall be true and correct on
the date of the Closing, with the same force and effect as if made on the date
of the Closing.

          6.2(b).  Compliance with Covenants. The Corporation shall have in all
material respects performed all obligations and agreements and complied with all
covenants contained in this Agreement to be performed and complied with by the
Corporation on or prior to the date of the Closing.

     6.3  Conditions to Obligations of the Corporation.

          The obligations of the Corporation to consummate the transactions
contemplated by this Agreement are subject to the satisfaction, on or before the
date of the Closing, of each of the following conditions precedent, any one or
more of which may be waived by the Corporation, in its sole and absolute
discretion:

          6.3(a).  Representations and Warranties. The representations and
warranties of Purchaser contained in this Agreement shall be true, correct and
complete in all material respects

<PAGE>   13
when made and shall be true and correct as of the date of the Closing with the
same force and effect as if made on the date of the Closing.

          6.3(b).  Compliance with Covenants. Purchaser shall have in all
material respects performed all obligations and agreements and complied with all
covenants contained in this Agreement to be performed and complied with by it on
or prior to the date of the Closing.

SECTION 7.  CLOSING.

     7.1  Deliveries by the Corporation.

          At the Closing, the Corporation shall deliver to Purchaser the
following:

               (1)  A certificate or certificates registered in Purchaser's
name, representing all of the Shares.

               (2)  A copy of the resolutions of the Board of Directors of the
Corporation, as certified as of the Closing Date by the Secretary of the
Corporation, as being true, correct and complete and then in full force and
effect, authorizing the execution, delivery and performance of this Agreement by
the Corporation, the authorization, sale, issuance and delivery of the Shares,
and the performance of the Corporation's obligations hereunder.

               (3)  A certificate of the Corporation signed by an authorized
officer of the Corporation certifying that the representations and warranties of
the Corporation made herein are true, complete and correct in all material
respects as of the date of this Agreement and are true and correct as of the
date of the Closing, and the Corporation has in all material respects performed
all obligations and agreements and complied with all covenants required to be
performed or complied with by the Corporation on or prior to the Closing.

               (4)  Such other certificates, instruments or documents as
Purchaser may reasonably request in order to effect and document the
transactions contemplated hereby.

     7.2  Deliveries by Purchaser.

          At the Closing, Purchaser shall deliver to the Corporation the
following:

               (1)  The Purchase Price, in cash or by wire transfer or certified
or bank cashier's check, payable to the order of the Corporation.

               (2)  A certificate of Purchaser signed by an authorized officer
of Purchaser, or such other officer satisfactory to the Corporation, certifying
that the representations and warranties of Purchaser made herein are true,
complete and correct in all material respects as of the date of this Agreement
and are true and correct as of the date of the Closing, and Purchaser has in all
material respects performed all obligations and agreements and complied with all
covenants required to be performed or complied with by Purchaser on or prior to
the Closing.

               (3)  Such other certificates, instruments or documents as the
Corporation may reasonably request in order to effect and document the
transaction contemplated hereby.

<PAGE>   14
Section 8. Legend.

     8.1  Endorsement.

          Each certificate representing the Shares shall bear the following
legend (in addition to any legend required by applicable state securities laws):

          THE SECURITIES REPRESENTED BY THIS CERTIFICATE HAVE NOT BEEN
     REGISTERED UNDER THE SECURITIES ACT OF 1933, AS AMENDED (THE "ACT") OR ANY
     OTHER FEDERAL OR STATE SECURITIES LAWS, AND MAY NOT BE SOLD, TRANSFERRED,
     ASSIGNED OR HYPOTHECATED UNLESS THERE IS AN EFFECTIVE REGISTRATION
     STATEMENT UNDER THE ACT AND ANY OTHER APPLICABLE FEDERAL SECURITIES LAWS
     COVERING SUCH SECURITIES OR THE CORPORATION RECEIVES AN OPINION OF COUNSEL
     IN FORM SATISFACTORY TO THE CORPORATION THAT AN EXEMPTION FROM SUCH
     REGISTRATION IS AVAILABLE.

     8.2  Removal of Legend.

          The legend endorsed on a stock certificate pursuant to Section 8.1 of
this Agreement shall be removed and the Corporation shall issue a certificate
without such legend to the holder of such Shares, if such Shares are registered
under applicable federal securities laws and a prospectus meeting the
requirements of the rules and regulations of the SEC is available or if such
holder provides to the Corporation an opinion of counsel to such holder
reasonably satisfactory to the Corporation, to the effect that a public sale,
transfer or assignment of such Shares may be made without registration and
without compliance with any restrictions.

SECTION 9.  TERMINATION.

     9.1  Mutual Consent.

          The parties may terminate this Agreement at any time by mutual written
agreement.

     9.2  Other Termination.

          The Corporation or the Purchaser may terminate this Agreement by
giving notice (a "Termination Notice") to the other parties at the time
designated in this Section or, in the absence of such designation, at any time
up to and including the date of the Closing, if any one or more of the following
shall have occurred and be continuing:

          9.2(a). Termination By Any Party. Any party may terminate this
Agreement under any one or more of the following circumstances:

               (1)  at any time after May 16, 1999, or, if the Corporation shall
have extended the Closing Date pursuant to Section 1.2(a) of this Agreement,
after July 16, 1999, if the Closing shall not have occurred for any reason other
than a default or non-performance of its obligations hereunder by the party
giving such notice;

               (2)  a court or other governmental authority of competent
jurisdiction shall have issued an order, writ, injunction or decree or shall
have taken any other action

<PAGE>   15
permanently restraining or otherwise prohibiting the purchase of the Shares
contemplated hereby and such order, writ, injunction, decree or other action
shall have become final and nonappealable.

          9.2(b).  Termination By Purchaser. Purchaser may terminate this
Agreement on the Closing Date, if any condition precedent set forth in Sections
6.1 or 6.2 shall not have been satisfied.

          9.2(c).  Termination By the Corporation. The Corporation may terminate
this Agreement on the Closing Date, if any condition precedent set forth in
Sections 6.1 or 6.3 shall not have been satisfied.

     9.3  Effect of Termination.

          Termination of this Agreement pursuant to this Section shall not
relieve any party of any liability for a default or other breach, default or
nonperformance under this Agreement. Notwithstanding the foregoing, no party
hereto shall be liable for consequential or punitive damages in connection with
such termination.

Section 10.  MISCELLANEOUS.

     10.1 Additional Actions and Documents.

          Each of the parties hereto agrees that it will, at any time, prior to,
at or after the Closing, take or cause to be taken such further actions, and
execute, deliver and file or cause to be executed, delivered and filed such
further documents and instruments (including export license applications) as may
be necessary or reasonably requested in connection with the consummation of the
purchase and sale contemplated by this Agreement or in order to fully effectuate
the purposes, terms and conditions of this Agreement.

     10.2 Expenses.

          Except as specified in Section 2, each party hereto shall pay its own
expenses incurred in connection with this Agreement and in the preparation for
and consummation of the transactions contemplated hereby.

     10.3 Notices.

          All notices, demands, requests, or other communications which may be
or are required to be given or made by any party to any other party pursuant to
this Agreement shall be in writing and shall be hand delivered, mailed by
first-class registered or certified mail, return receipt requested, postage
prepaid, or delivered by overnight air courier, addressed as follows:

          (i)  if to the Corporation:

          Security First Technologies Corporation
          3390 Peachtree Road, NE, Suite 1700
          Atlanta, Georgia 30326
          Attn.: President

          with a copy (which shall not constitute notice) to:

<PAGE>   16
            Hogan & Hartson L.L.P.
            555 Thirteenth Street, N.W.
            Washington, D.C. 20004
            Attn.: Stuart G. Stein, Esq.

            (iii)   if to Purchaser:

            AC II Technology (ACT II) B.V.
            1661 Page Mill Road
            Palo Alto, CA 94304
            Attn.: Chief Financial Officer

            with a copy (which shall not constitute notice) to:

            Andersen Consulting LLP
            1661 Page Mill Road
            Palo Alto, CA 94304
            Attn.: General Counsel

or such other address as the addressee may indicate by written notice to the
other parties. Each notice, demand, request, or communication which shall be
given or made in the manner described above shall be deemed sufficiently given
or made for all purposes at such time as it is delivered to the addressee (with
the return receipt, the delivery receipt, or the affidavit of messenger being
deemed conclusive but not exclusive evidence of such delivery) or at such time
as delivery is refused by the addressee upon presentation.

     10.4 Waiver.

          No waiver by any party of any failure or refusal of any other party to
comply with its obligations under this Agreement shall be deemed a waiver of any
other or subsequent failure or refusal to so comply by such other party. No
waiver shall be valid unless in writing signed by the party to be charged and
only to the extent therein set forth.

     10.5 Binding Effect.

          This Agreement shall be binding upon and shall inure to the benefit of
the parties hereto and their respective successors and assigns.

     10.6 Entire Agreement; Amendment.

          This Agreement, including the other instruments and documents referred
to herein or delivered pursuant hereto, contains the entire agreement among the
parties with respect to the subject matter hereof and supersedes all prior oral
or written agreements, commitments or understandings with respect to such
matters. No amendment, modification or discharge of this Agreement shall be
valid or binding unless set forth in writing and duly executed by the party
against whom enforcement of the amendment, modification or discharge is sought.

     10.7 Severability.

          If any part of any provision of this Agreement shall be invalid or
unenforceable under applicable law, such part shall be ineffective to the extent
of such invalidity or unenforceability only,

<PAGE>   17
without in any way affecting the remaining parts of such provisions or the
remaining provisions of said Agreement.

     10.8  Headings.

           The headings of the sections and subsections contained in this
Agreement are inserted for convenience only and do not form a part or affect the
meaning, construction or scope thereof.

     10.9  Governing Law.

           This Agreement, the rights and obligations of the parties hereto, and
any claims or disputes relating thereto, shall be governed by and construed
under and in accordance with the laws of the State of Delaware, excluding the
choice of law rules thereof.

    10.10  Signature in Counterparts.

           This Agreement may be executed in separate counterparts, none of
which need contain the signatures of all parties, each of which shall be deemed
to be an original, and all of which taken together constitute one and the same
instrument. It shall not be necessary in making proof of this Agreement to
produce or account for more than the number of counterparts containing the
respective signatures of, or on behalf of, all of the parties hereto.

    10.11  No Third Party Beneficiaries.

           Except as expressly provided herein, this Agreement is made and
entered into for the sole protection and benefit of the parties hereto, and no
other person or entity shall have any right of action hereon, right to claim any
right or benefit from the terms contained herein or be deemed a third party
beneficiary hereunder.

    10.12  Assignability.

           All terms and provisions of this Agreement shall be binding upon and
inure to the benefit of the parties hereto, and their respective transferees,
successors and assigns; provided, however, that neither this Agreement nor any
rights, privileges, duties and obligations of the parties hereto may be assigned
or delegated by any party hereto without the prior written consent of all the
parties to this Agreement and any such purported or attempted assignment shall
be null and void ab initio and of no force or effect provided, further that
Purchaser may assign this Agreement, including rights, privileges, duties and
obligations hereunder to any affiliate of Purchaser which is wholly or
substantially owned directly or indirectly by Purchaser so long as such
assignment does not in any way materially delay or otherwise materially
adversely impact the ability of the parties hereto to effect the transactions
contemplated hereby.

    10.13  Parties Not Partners.

           Nothing contained in this Agreement shall constitute any party as a
partner with, agent for or principal of any one or more of the other parties or
their successors and assigns

                            [SIGNATURE PAGE FOLLOWS]
<PAGE>   18
          IN WITNESS WHEREOF, the parties hereto have caused this Agreement to 
be duly executed and delivered as of the date first above written.


                                         SECURITY FIRST TECHNOLOGIES CORPORATION


                                         By:            /s/ Robert F. Stockwell
                                            ------------------------------------
                                              Name:     Robert F. Stockwell
                                                   -----------------------------
                                              Title:    Chief Financial Officer
                                                    ----------------------------
                                                        & Treasurer
                                                    ----------------------------

                                         
                                         AC II TECHNOLOGY (ACT II) B.V.


                                         By:         /s/ Michael L. Emmons
                                            ------------------------------------
                                              Name:  Michael L. Emmons
                                                   -----------------------------
                                              Title: Director
                                                    ----------------------------