<PAGE>
                                                                   EXHIBIT 10.31
                      ASSIGNMENT AND ASSUMPTION OF LEASE

        The Assignment and Assumption of Lease (this "Agreement") is executed as
of July 10, 2001, by and among AmberJack, Ltd. ("Landlord"), Integrated
Information Systems, ("Tenant/Assignor") and The CIT Group/Equipment Financing,
Inc. ("Assignee").

        WHEREAS, the Landlord and Tenant/Assignor are parties to that certain
Lease dated April 25 1997 (as amended, the "Lease"), for premises located at
1560 W. Fountainhead Parkway, Suites 100 and 150, Tempe, AZ, 85252, pursuant to
which Landlord leases to Tenant/Assignor, and Tenant/Assignor leases form
Landlord, the real property described in the Lease (the "Property"). A copy of
the Lease (together with any amendments thereto) is attached hereto as Exhibit
                                                                       -------
A.
--

        WHEREAS, Tenant/Assignor seeks to assign and transfer all of its rights
and obligations under the Lease to Assignee and Assignee seeks to succeed to all
of such rights and assume all of such obligations, all upon the terms and
conditions hereinafter set forth.

        NOW, THEREFORE, for valuable consideration, the receipt and sufficiency
of which are hereby acknowledged, the parties agree as follows:

        1.   This Agreement shall be effective August 1, 2001. (The "Effective
             Date")

        2.   Tenant/Assignor hereby assigns and transfers to Assignee, and
             Assignee hereby accepts, all of Tenant/Assignor's right, title and
             Interest under the Lease and in connection with the Property
             (including, subject to the terms of the Lease, any and all
             improvements and fixtures located on the Property, and any and all
             rights, privileges, easements, rights-of-way and appurtenances
             Appertaining to or in connection with the Property).

        3.   Assignee hereby assumes all of Tenant/Assignor's duties,
             commitments and obligations under the Lease arising after the
             Effective Date.

        4.   Landlord hereby approves of, and consents to, the Assignment and
             Assumption set forth in paragraphs 2 and 3 hereof and releases
             Tenant/Assignor for any obligation occurring after the Effective
             Date.

        5.   All charges due to the Landlord for services and all claims and
             liabilities related to the Lease incurred on or before the
             Effective
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        Date shall be responsibility of Tenant/Assignor and all charges due to
        the Landlord for services and all claims and liabilities related to the
        Lease incurred after Effective Date shall be the responsibility of
        Assignee.

    6.  Tenant/Assignor agrees to and does hereby indemnify and hold Assignee
        harmless from and against all charges due to the Landlord for services
        and all claims and liabilities related to the Lease arising on or before
        the Effective Date.

    7.  Assignee agrees to and does hereby indemnify and hold Tenant/Assignor
        harmless from and against all charges due to the Landlord for services
        and all claims and liabilities related to the Lease arising after the
        Effective Date.

    8.  This Assignment Agreement shall be governed by Arizona Law. This
        Agreement constitutes the complete agreement of the parties relating to
        the subject matter hereof and supersedes any prior agreements or
        understandings. This Agreement may not be amended unless agreed upon in
        writing by all parties. The provisions of this Agreement shall be
        binding upon and inure to the benefit of Integrated Information Systems
        and The CIT Group/Equipment Financing, Inc. and their respective
        successors and assigns.

    9.  Effective August 1 2001, Tenant/Assignor shall pay to Assignee
        $38,409.88 per month, due and payable on the 1st day of each month from
        August 1 2001 until December 1 2001. The five monthly payments shall
        total $192,049.40.

    10. Tenant/Assignor is responsible for the payment of any and all lease
        commissions in connection with this transaction. Such commissions are
        described in a separate agreement between Tenant/Assignor and it's
        Agent.

    11. Tenant/Assignor is not required to remove any of the existing interior
        improvements within the leased premises, or replace or restore any
        previous interior improvements within the leased premises at the end of
        the lease term. Tenant/Assignor shall deliver the leased premises to
        Assignee in its existing configuration and condition, normal wear and
        tear excluded.

                                  End of Page


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IN WITNESS WHEREOF, the Landlord, Tenant/Assignor and Assignee have executed
this Agreement as of the date first written above.


"TENANT/ASSIGNOR"                               "ASSIGNEE"

Integrated Information Systems                  The CIT Group/Equipment
                                                Financing, Inc.

By:  /s/ DARRYL S. BAKER                        By:  /s/ RAY HENDON
   ------------------------------                  ----------------------------

Its:  Controller                                Its:  SVP/CFO
    -----------------------------                   ---------------------------

Date:   7/10/01                                 Date:   7/10/01
     ----------------------------                    --------------------------

"LANDLORD"

Birtcher Arizona, LLC
Manager for AmberJack, Ltd.

By:   /s/ THEODORE RABAN
   ------------------------------

Its:    Manager
    -----------------------------

Date:   7/10/01
     ----------------------------