<PAGE>   1





                                                                    Exhibit 4.06

                AMENDMENT NO. 1 TO REGISTRATION RIGHTS AGREEMENT

     This Amendment No. 1 to Registration Rights Agreement (this "AMENDMENT")
is made and entered into as of February 24, 1997, by and between HNC Software
Inc., a Delaware corporation ("HNC"), St. George's Trust Company Limited, as
Trustee of The Mulberry Trust ("MULBERRY"), St.  George's Trust Company
Limited, as Trustee of The Kulmor Trust ("KULMOR"), Miurkirk Investments Ltd.,
a company incorporated under the laws of the Commonwealth of the Bahamas
("MIURKIRK") and Oyster Pursuits Ltd., a company incorporated under the laws of
the Commonwealth of the Bahamas ("OYSTER")

                                R E C I T A L S

         A.      HNC, Mulberry and Kulmor previously entered into a certain
Registration Rights Agreement dated as of October 25, 1996 (the "REGISTRATION
RIGHTS AGREEMENT") in connection with the issuance of shares of HNC's Common
Stock to Mulberry and Kulmor pursuant to an Exchange Agreement dated as of
October 25, 1996 (the "EXCHANGE AGREEMENT").

         B.      Mulberry has privately transferred to Miurkirk One Million One
Hundred Sixty-Two Thousand One Hundred Seventeen (1,162,117) shares of HNC's
Common Stock (the "MULBERRY SHARES") that Mulberry acquired pursuant to the
Exchange Agreement.

         C.      Kulmor has privately transferred to Oyster Two Hundred Five
Thousand Seventy-Nine (205,079) shares of HNC's Common Stock (the "KULMOR
SHARES") that Kulmor acquired pursuant to the Exchange Agreement.

         D.      Mulberry desires to assign its rights under the Registration
Rights Agreement with respect to the Mulberry Shares to Miurkirk, which is
wholly-owned by Mulberry, and Kulmor desires to assign its rights under the
Registration Rights Agreement with respect to the Kulmor Shares to Oyster,
which is wholly-owned by Kulmor, and HNC desires to permit such assignment.

         NOW, THEREFORE, the parties hereto hereby agree as follows:

         1.      ACKNOWLEDGMENT; CERTAIN TERMS.  Each party to this Amendment
acknowledges that it has reviewed and understood the terms and conditions of
the Registration Rights Agreement.  Unless otherwise expressly defined in this
Amendment, all capitalized terms used in this Amendment will have the same
meanings given to such terms in the Registration Rights Agreement.

         2.      ASSIGNMENT AND ASSUMPTION AND CONSENT.

                 (a)      Mulberry and Miurkirk.  Mulberry hereby assigns and
transfers to Miurkirk all of Mulberry's rights, duties, obligations and
responsibilities under the Registration Rights Agreement, and, in consideration
of such assignment and transfer and the consents and agreements of HNC herein,
Miurkirk hereby agrees with HNC to assume all Mulberry's duties, obligations
and responsibilities under the Registration Rights Agreement (including without
limitation all such duties, obligations and responsibilities that arose prior
to the date of this Amendment) and to be bound by all of the terms and
<PAGE>   2
conditions of the Registration Rights Agreement as a party thereto (including
but not limited to the indemnification provisions of Section 1.9 of the
Registration Rights Agreement).

                 (b)      Kulmor and Oyster.  Kulmor hereby assigns and
transfers to Oyster all of Kulmor's rights, duties, obligations and
responsibilities under the Registration Rights Agreement, and, in consideration
of such assignment and transfer and the consents and agreements of HNC herein,
Oyster hereby agrees with HNC to assume all Kulmor's duties, obligations and
responsibilities under the Registration Rights Agreement (including without
limitation all such duties, obligations and responsibilities that arose prior
to the date of this Amendment) and to be bound by all of the terms and
conditions of the Registration Rights Agreement as a party thereto (including
but not limited to the indemnification provisions of Section 1.9 of the
Registration Rights Agreement).

                 (c)      Consent.  In consideration of the agreements of
Miurkirk and Oyster herein, HNC hereby consents to: (i) the assignment and
transfer to Miurkirk of Mulberry's rights, duties, obligations and
responsibilities under the Registration Rights Agreement with respect to the
Mulberry Shares; and (ii) the assignment and transfer to Oyster of Kulmor's
rights, duties, obligations and responsibilities under the Registration Rights
Agreement with respect to the Kulmor Shares.

         3.      AMENDMENTS.  The Registration Rights Agreement is hereby
amended as follows (and by signing this Amendment, Miurkirk and Oyster each
agree to be bound by all of the following provisions of this Section 3):

                 (a)      Shareholders.  Miurkirk and Oyster shall each become
parties to the Registration Rights Agreement as "Shareholders" thereunder (and
Mulberry and Kulmor shall cease to be parties to the Registration Rights
Agreement).  Miurkirk and Oyster agree that they shall each be bound by all of
the rights, duties, and obligations applicable to Shareholders under the
Registration Rights Agreement and by all of the terms and conditions of the
Registration Rights Agreement.  The term "Shareholders" as used in the
Registration Rights Agreement, shall mean Miurkirk and Oyster, collectively and
the term "Shareholder" as used in the Registration Rights Agreement, shall mean
either Miurkirk or Oyster, individually.

                 (b)      Registrable Securities.  The parties acknowledge and
agree that the shares of HNC Common Stock referred to in Section 1.1(d)(i) of
the Registration Rights Agreement are the Mulberry Shares and the Kulmor
Shares, as defined in the recitals to this Amendment.

                 (c)      Exhibit A.  Exhibit A to the Registration Rights
Agreement will be amended and restated in its entirety as set forth in Exhibit
A to this Amendment.

         4.      MISCELLANEOUS.

                 (a)      Material Inducements.  Miurkirk and Oyster understand
that their agreements under this Amendment are material inducements to HNC to
enter into this Amendment.

                 (b)      Counterparts.  This Amendment may be executed in any
number of counterparts, each of which when so executed and delivered will be
deemed to be an original and all of which taken together will constitute one
and the same instrument.

                 (c)      Effect of Amendment.  Except as amended hereby, the
Registration Rights Agreement remains in full force and effect.  In the event
of any conflict between this Amendment and the Registration Rights Agreement,
this Amendment will control and govern.



                                       -2-
<PAGE>   3
                 IN WITNESS WHEREOF, the undersigned parties have executed this
Amendment effective as of the date and year first above written.

                 HNC SOFTWARE INC.
MIURKIRK INVESTMENTS LTD.


By: _____________________________             By: _____________________________
Name: ___________________________             Name: ___________________________
Title: __________________________             Title: __________________________


THE MULBERRY TRUST                            OYSTER PURSUITS LTD.

By: St. George's Trust Company Limited, 
as Trustee

By: _____________________________             By: _____________________________
Name: ___________________________             Name: ___________________________
Title: __________________________             Title: __________________________


THE KULMOR TRUST
By: St. George's Trust Company Limited, 
as Trustee

By: ______________________________
Name: ____________________________
Title: _____________________________


ATTACHMENTS:

Exhibit A        List of Shareholders





         [SIGNATURE PAGE TO AMENDMENT TO REGISTRATION RIGHTS AGREEMENT]





                                        -3-
<PAGE>   4
                                   EXHIBIT A

                              LIST OF SHAREHOLDERS


<TABLE>
<CAPTION>
                                                      Number of Shares of HNC
Name and Address                                         Common Stock Held
----------------                                         -----------------
<S>                                                          <C>
Miurkirk Investments Ltd.                                     1,162,117
   4th Floor, 33 Reid Street
   Hamilton, Bermuda

Oyster Pursuits Ltd.                                            205,079
   4th Floor, 33 Reid Street
   Hamilton, Bermuda
</TABLE>