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                                                                    EXHIBIT 5.01


                                February 9, 2001



HNC Software Inc.
5935 Cornerstone Court West
San Diego, CA  92121-3728

Gentlemen/Ladies:

        At your request, we have examined the Registration Statement on Form S-8
(the "REGISTRATION STATEMENT") to be filed by HNC Software Inc., a Delaware
corporation (the "COMPANY"), with the Securities and Exchange Commission (the
"COMMISSION") on or about February 12, 2001, in connection with the registration
under the Securities Act of 1933, as amended, of an aggregate of 322,892 shares
of the Company's Common Stock, $0.001 par value (the "SHARES"), that are subject
to issuance by the Company upon the exercise of stock purchase rights to be
granted by the Company's under its 1995 Employee Stock Purchase Plan, as amended
(the "PURCHASE PLAN").

        In rendering this opinion, we have examined the following:

        (1)    the Company's Restated Certificate of Incorporation, as amended,
               and Amendment to Certificate of Incorporation, both certified by
               the Delaware Secretary of State on February 9, 2001;

        (2)    the Company's Bylaws, as amended, certified by the Company's
               Assistant Secretary on February 9, 2001.;

        (3)    the Registration Statement, together with the exhibits filed as a
               part thereof or incorporated therein by reference;

        (4)    the prospectus prepared in connection with the Registration
               Statement;

        (5)    the minutes of meetings and actions by written consent of the
               stockholders and Board of Directors that are contained in the
               Company's minute books that are in our possession;

        (6)    a certificate from the Company's transfer agent dated February 5,
               2001, verifying the number of the Company's issued and
               outstanding shares of capital stock as of December 31, 2000;

        (7)    a statement from the Company as to the number of outstanding
               options, warrants and rights to purchase the Company's capital
               stock and any additional shares of the Company's Common Stock
               reserved for future issuance in connection with the Company's
               stock option and purchase plans and all other plans, agreements
               or rights as of December 31, 2000; and

        (8)    a Management Certificate addressed to us and dated of even date
               herewith executed by the Company and containing certain factual
               and other representations (the "MANAGEMENT CERTIFICATE").

        In our examination of documents for purposes of this opinion, we have
assumed, and express no opinion as to, the genuineness of all signatures on
original documents, the authenticity and completeness of all documents submitted
to us as originals, the conformity to originals and completeness of all
documents submitted to us as copies, the legal capacity of all persons or
entities executing the same, the lack of any undisclosed termination,
modification, waiver or amendment to any document reviewed by us and the due
authorization, execution and delivery of all documents where due authorization,
execution and delivery are prerequisites to the effectiveness thereof.


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        As to matters of fact relevant to this opinion, we have relied solely
upon our examination of the documents referred to above and have assumed the
current accuracy and completeness of the information obtained from the documents
referred to above and the representations and warranties made by representatives
of the Company to us, including but not limited to those set forth in the
Management Certificate. We have made no independent investigation or other
attempt to verify the accuracy of any of such information or to determine the
existence or non-existence of any other factual matters; however, we are not
aware of any facts that would cause us to believe that the opinion expressed
herein is not accurate.

        We are admitted to practice law in the State of California, and we
render this opinion only with respect to, and express no opinion herein
concerning the application or effect of the laws of any jurisdiction other than,
the existing laws of the United States of America and, with respect to the
validity of corporate action and the requirements for the issuance of stock, of
the State of Delaware.

        Based upon the foregoing, it is our opinion that the 322,892 Shares that
may be issued and sold by the Company upon the exercise of purchase rights to be
granted under the Purchase Plan, when issued, sold and delivered in accordance
with the Purchase Plan and the purchase agreements to be entered into thereunder
and in the manner and for the consideration stated in the Registration Statement
and the relevant Prospectus, will be validly issued, fully paid and
nonassessable.

        We consent to the use of this opinion as an exhibit to the Registration
Statement and further consent to all references to us, if any, in the
Registration Statement, the Prospectus constituting a part thereof and any
amendments thereto. This opinion speaks only as of its date and we assume no
obligation to update this opinion should circumstances change after the date
hereof. This opinion is intended solely for use in connection with the issuance
and sale of Shares subject to the Registration Statement and is not to be relied
upon for any other purpose.



                                            Very truly yours,

                                            /s/ FENWICK & WEST LLP

                                            FENWICK & WEST LLP