<PAGE>

                                                                    EXHIBIT 99.8

ADVANCED INSTRUCTION TO SELL COMMON STOCK

To: Deutsche Bank Alex. Brown
    A Division of Deutsche Bank Securities Inc.

Account Number:                                          Date:  October 31, 2003

         I am a holder of shares, or options to acquire shares, of the common
stock ("Common Stock") of RSA Security Inc. (the "Company"). I would like to
periodically sell Company shares in order to diversify my portfolio. I also wish
to take advantage of Rule 10b5-1 under the Securities Exchange Act of 1934, as
amended, which provides for an affirmative defense from insider trading
liability for purchases and sales effected pursuant to a contract, instruction
or plan entered into when a person is not aware of any material nonpublic
information. This instruction ("Instruction") is intended to constitute a
"written plan for trading securities" within the meaning of Rule 10b5-1.

         I hereby instruct Deutsche Bank Securities Inc. (referred to herein as
"Deutsche Bank Alex. Brown") for the period commencing January 1, 2004 and
terminating on December 31, 2004 as follows:

         For the first month of each quarter, no shares should be sold until 48
hours after the Company's earnings are publicly released. In addition, no sales
should occur during the last three weeks of each quarter (i.e. no sales should
take place during the Company's trading blackout period).

     i)   With respect to any stock options with an exercise price equal to
          $4.42 per share, exercise and simultaneously sell 50% of all vested
          options if the Company's Common Stock is trading at a price equal to
          $10.42 per share or higher; if the Company's Common Stock is trading
          at a price equal to $12.42 per share or higher, sell up to 75% of all
          vested shares; and if the Company's Common Stock is trading at a price
          equal to $14.42 per share or higher, sell all vested shares.

     ii)  With respect to any stock options with an exercise price equal to
          $4.04 per share, exercise and simultaneously sell 50% of all vested
          options if the Company's Common Stock is trading at a price equal to
          $10.04 per share or higher; if the Company's Common Stock is trading
          at a price equal to $12.04 per share or higher, sell up to 75% of all
          vested shares; and if the Company's Common Stock is trading at a price
          equal to $14.04 per share or higher, sell all vested shares.

     iii) With respect to any stock options with an exercise price equal to
          $8.04 per share, exercise and simultaneously sell 5,000 vested options
          per quarter if the Company's Common Stock is trading at a price equal
          to $14.04 per share or higher.

<PAGE>

         You are authorized to make deliveries of securities and payment of
moneys in accordance with your normal practice. All shares to be sold shall have
been previously deposited into my account, and you shall not be required to
follow this Instruction if shares are not present in my account (or acceptable
arrangements to deliver option shares have not been made) prior to the dates on
which sales shall occur. If this Instruction requires you to exercise stock
options you shall do so in accordance with your normal procedures, and unless
instructed otherwise, remit the exercise price and the withholding tax as
calculated by the Company. The share amount listed above shall be increased or
decreased to reflect stock splits should they occur. I understand that I shall
be responsible to arrange for any filings that may be required under applicable
law (e.g., Form 144, Schedule 13D, and Forms 4 and 5), and that I may be subject
to the short swing profit rules contained in Section 16 of the Securities
Exchange Act of 1934. In this connection, I understand that upon my request, you
will assist me in making advance arrangements regarding the filing of Forms 144;
provided that you agree to notify me and the following representatives of RSA's
legal department within eight hours of making any trade so that I may file the
required Form 4 in a timely fashion:

          -    Margaret Seif: Phone: 781-515-5403; email: mseif@rsasecurity.com

          -    Kathryn Leach: Phone: 781-515-5422; email: kleach@rsasecurity.com

          -    Chris Dollase: Phone: 781-515-5507; email:
               cdollase@rsasecurity.com

         All sales shall be effected in your normal fashion in accordance with
your terms and conditions for my account and risk. You may act as principal in
any transaction hereunder. I understand that you may not be able to make all of
the sales contemplated under this Instruction due to a market disruption or a
legal, regulatory or contractual restriction applicable to you or any other
event or circumstance. I further understand that even in the absence of such a
circumstance, you may be unable to make sales consistent with ordinary
principles of best execution due to insufficient volume of trading or other
market factors in effect on the date of a sale. I hereby ratify and confirm any
and all transactions with you in accordance with this Instruction. I also agree
to indemnify and hold Deutsche Bank Alex. Brown harmless from any and all losses
arising from any cause of action arising from its performance of this
Instruction. For purposes of this Section, the term "losses" shall mean monetary
damages for which a court or regulatory agency has found Deutsche Bank to be
finally liable, after all appeals have been exhausted, but which shall in no
event exceed an amount equal to the proceeds received by You in connection with
exercises of stock options pursuant to this Instruction. Notwithstanding the
foregoing, "losses" shall not include Deutsche Bank's attorneys fees, and
Deutsche Bank may not settle any action for which it will claim indemnification
from you without your prior written consent.

         You will cease making sales under this Instruction as soon as
practicable following receipt of written notice from the Company, confirmed by
telephone, that the Company has entered into a transaction that results in my
being subject to trading restrictions. You shall resume making sales in
accordance with this Instruction as soon as practicable after you receive
written notice from the Company of the cessation or termination of any such
trading restriction. Any sales not made as a result of the imposition of any
trading restriction shall be sold in the next following selling period.

<PAGE>

         While this Instruction is in effect I will not enter into or alter any
corresponding or hedging transaction or position with respect to the Common
Stock (including any securities convertible or exchangeable into Common Stock).

         I represent and warrant that I am not presently aware of any material
nonpublic information regarding the Company or its securities and that I am
currently able to sell Common Stock under the Company's insider trading policies
and covenant that I will not discuss or otherwise disclose material nonpublic
information to my investment representative or any other of your personnel
responsible for carrying out this Instruction. I have obtained the approval of
the Company's counsel to enter into this Instruction.

         This Instruction may be modified, terminated or amended only by a
writing signed by the parties hereto. Any modification or amendment of this
Instruction may only occur at a time when I am not aware of material nonpublic
information concerning the Company or its securities and I am otherwise
permitted to make sales under the Company's insider trading policies. If this
Instruction is modified or amended, or if I establish a new plan after
termination of this Instruction, no sales shall be made during the thirty (30)
calendar days immediately following such modification, amendment or termination
(other than sales already provided for in the Instruction prior to modification,
amendment or termination).

         This Instruction shall not be effective until Deutsche Bank Alex. Brown
confirms its acceptance in writing by signing below. It shall remain in full
force and effect until revoked or modified by me in writing. Deutsche Bank Alex.
Brown may decline to act hereunder upon reasonable notice. I hereby irrevocably
authorize you to accept any instruction from the Company to cease or suspend
sales hereunder.

                                                             /s/Margaret K. Seif
                                                             -------------------
                                                             Margaret K. Seif

--------------------------------------------------------------------------------
Accepted
Deutsche Bank Alex. Brown

/s/Nancy Mehan for Stuart Williams
-----------------------------------------
Branch Manager

Dated: 10/30/03

<PAGE>

                                   SCHEDULE A
                             (Shares Owned Outright)

Name of Seller:           Seller's Social Security #
               ----------                            -------
Daytime Tel. #:              Cellular:          Fax #:           Email
               ----------              ----------      ----------      ---------

SALE OF OWNED STOCK

<TABLE>
<CAPTION>
        a.                                                   b.                                       c.
Designated Sale Period                              Authorized Number of                    Net Limit Price ($) or
       From                        To                   Owned Shares                     "Market" Price (select one):
-----------------------    ---------------------   ----------------------               -----------------------------
<S>                        <C>                     <C>                                  <C>
                                                                                         $
----------------------------------------------------------------------------------------------------------------------

                                                                                         $
----------------------------------------------------------------------------------------------------------------------

                                                                                         $
----------------------------------------------------------------------------------------------------------------------

                                                                                         $
----------------------------------------------------------------------------------------------------------------------

                                                                                         $
----------------------------------------------------------------------------------------------------------------------

                                                                                         $
----------------------------------------------------------------------------------------------------------------------

                                                                                         $
----------------------------------------------------------------------------------------------------------------------

                                                                                         $
----------------------------------------------------------------------------------------------------------------------
</TABLE>

                                     TOTAL:

1.   INSTRUCTIONS: In column (a), state the first and last date on which the
     Shares are authorized to be sold during the Designated Sale Period (Stock
     sales may occur on or between these dates). The "To" column may be left
     blank in which case the Designated Sale Period will last until this
     Instruction terminates.

     In column (b), state the maximum number of shares authorized to be sold at
     the designated price during the Designated Sale Period. Do not aggregate
     with amounts authorized to be sold at a lower price during the same
     Designated Sale Period.

     In column (c), write either (i) a dollar price which is the minimum price
     (the "Net Limit Price") at which Stock is authorized to be sold, or (ii)
     the word "market" if Stock is to be sold at the then-prevailing market
     price per share during the Designated Sale Period. If a Net Limit Price is
     instructed, I understand that my order(s) will be executed only when
     Deutsche Bank Alex. Brown can sell at a price equal or higher than my
     minimum price(s) plus the mark-up.

2.   In the event that Deutsche Bank Alex. Brown is unable to sell the
     Authorized Number of Owned Shares in a Designated Sale Period for any
     reason: (check one of the following instructions)

          the unsold amount of Stock will be carried forward and added to the
     ---
          Authorized Number of Owned Shares for each succeeding Designated Sale
          Period until sold at the original net limit price; or

          the unsold amount of Stock will not be sold and will not be carried
     ---
          over to the next Designated Sale Period.

3.   I    am (      am not) subject to Rule 144 filing requirements and, if
       ---    -----
     applicable, I have provided signed documents to be filed on my behalf.

<PAGE>

                                   SCHEDULE B
                                 (Stock Options)
                         TO MARGARET K. SEIF 1-b5-1 PLAN
                             DATED OCTOBER 31, 2003

Name of Seller: Margaret Seif        Seller's Social Security #
Daytime Tel. #:          Cellular:          Fax #:          Email:
                --------           --------        --------

    EXERCISE OF OPTIONS AND SALE OF STOCK OBTAINED UPON EXERCISE OF OPTIONS.

     (Please note: Seller represents that the information below is accurate. You
     may use multiple lines to apportion shares in a grant across differing
     Sales Periods or Limit Prices. Each line will be treated as a distinct
     trading instruction.).

<TABLE>
<CAPTION>
-------------- ------------ ------------ ------------- ------------- ------------------- --------------------- -----------------
                                                        d.                                                          g.
                                                      Vesting             e.                                  Net Limit Price
                            b.          c.            Date For      Designated Sale            f.             ($) or "Market"
               a.         Date of      Strike         Unvested           Period          Authorized Number    Price (select
 LINE      Grant ID #      Grant        Price          Shares        From       To       of Option Shares           one):
---------  ----------    ---------     -------       -----------   -----------------     ------------------   -------------------
<S>        <C>           <C>           <C>           <C>           <C>                   <C>                  <C>
 1         R98-1488      6/18/02       4.42           9/18/02       1/1/04   12/31/04           2,092            $10.42
           (NQ)                                       (131)

------------------------------------------------------------------------------------------------------------------------------------
 2         R98-1488A     6/18/02       4.42           9/18/02       1/1/04   12/31/04          42,907            $10.42
           (NQ)                                       (2,682)

------------------------------------------------------------------------------------------------------------------------------------
 3         R98-313A      6/18/02       4.42           9/18/02       1/1/04   12/31/04          16,873            $10.42
           (NQ)                                       (1,055)

------------------------------------------------------------------------------------------------------------------------------------
 4         R94-1025      6/18/02       4.42           9/18/02       1/1/04   12/31/04           6,703            $10.42
           (NQ)                                       (419)

------------------------------------------------------------------------------------------------------------------------------------
 5         R94-1025A     6/18/02       4.42           9/18/02       1/1/04   12/31/04          51,196            $10.42
           (NQ)                                       (3,200)

------------------------------------------------------------------------------------------------------------------------------------
 6         94-1029       7/10/02       4.04           7/10/03       1/1/04   12/31/04          93,006            $10.04
           (ISO)                                      (24,752)

------------------------------------------------------------------------------------------------------------------------------------
 7         94-1029A      7/10/02       4.04           7/10/03       1/1/04   12/31/04           6,994            $10.04
           (NQ)                                       (248)

------------------------------------------------------------------------------------------------------------------------------------
 8         R94-557       8/12/98       8.04           Fully vested  1/1/04   12/31/04           5,182            $14.04
           (ISO)

------------------------------------------------------------------------------------------------------------------------------------
 9         R94-902       8/12/98       8.04           Fully vested  1/1/04   12/31/04          23,438            $14.04
           (NQ)

------------------------------------------------------------------------------------------------------------------------------------
10         R94-557A      8/12/98       8.04           Fully vested  1/1/04   12/31/04          14,605            $14.04

------------------------------------------------------------------------------------------------------------------------------------
</TABLE>

                                 TOTAL: 262,996

         INSTRUCTIONS:

         1. In columns (a) and (b), list the Options which are to be exercised.

            In column (c), specify the applicable strike price.

            In column (d) specify the applicable vesting date.

<PAGE>

         In column (e), state the first and last date on which the option is
         authorized to be exercised and sold during the Designated Sale Period
         (Exercises and sales may occur on or between these dates). The "To"
         column may be left blank in which case the Designated Sale Period will
         last until this Instruction terminates.

         IN COLUMN (F), STATE THE MAXIMUM NUMBER OF OPTION SHARES TO BE
         EXERCISED.

         IN COLUMN (G), WRITE THE DOLLAR PRICE WHICH IS THE MINIMUM PRICE (THE
         "NET LIMIT PRICE") AT WHICH THE AUTHORIZED NUMBER OF OPTION SHARES IS
         AUTHORIZED TO BE SOLD. IF A NET LIMIT PRICE IS INSTRUCTED, I UNDERSTAND
         THAT MY ORDER(S) WILL BE EXECUTED ONLY WHEN DEUTSCHE BANK ALEX. BROWN
         SELLS AT A PRICE EQUAL OR HIGHER THAN MY MINIMUM PRICE(S) PLUS THE
         MARK-UP.

2.       In the event that Deutsche Bank Alex. Brown is unable to sell the
         Authorized Number of Option Shares in a Designated Sale Period for any
         reason: (check one of the following instructions)

         X the unsold amount of Option Shares will be carried forward and added
         to the Authorized Number of Option Shares for each succeeding
         Designated Sale Period until sold at the original net limit price; or

         ___ the unsold amount of Option Shares will not be sold and will not be
         carried over to the next Designated Sale Period.

3.       I X am (_____ am not) subject to Rule 144 filing requirements and, if
         applicable, I have provided signed documents to be --- filed on my
         behalf.

4.       I recognize that if the nature of the above listed options changes
         materially, including but not limited to my termination, I will notify
         Deutsche Bank Alex. Brown immediately.