<PAGE>

                                                                 EXHIBIT 10.23.1

                           FIRST AMENDMENT OF LEASE

     This First Amendment of Lease is made as of this 20th day of April, 1998,
by and between Lot 4 LLC (hereinafter referred to as "Landlord"), and Acorn
Information Services, Inc., of Fairfield, Connecticut (hereinafter referred to
as "Tenant").

     In consideration of the mutual benefits and obligations set forth herein,
the parties hereby amend a certain lease between Landlord and Tenant dated
January 5, 1998, for the lease of space in Landlord's building at 4 Corporate
Drive, Shelton, Connecticut (the January 5, 1998 lease as amended, hereinafter
referred to collectively as the "Lease"), in the following manner:

     A.   Paragraph 1.1 (b) of the Lease is deleted and is replaced with the
          following:

               "1.1 (b) The "Leased Premises" is located on the second floor of
               the Building, with the floor area outline of the Leased Premises
               being shown on Exhibit A, attached hereto."

     B.   Paragraph 1.1 (c) of the Lease is deleted and is replaced with the
          following:

               "1.1 (c) The "Leased Premises Square Footage" is 7,166 square
               feet."

     C.   Exhibit A is added to the Lease and is attached to this First
          Amendment of Lease.

     In the event of any conflict between this First Amendment of Lease and the
January 5, 1998 lease, this First Amendment of Lease shall control, the Lease
being hereby ratified and to remain in full force and effect in all other
respects.


     IN WITNESS WHEREOF, the parties have hereunto set their hands and seals as
     of the day and year first above written.


                                     Acorn Information Services, Inc


                                     By: /s/ Venkat Sharma
                                         -----------------
                                         Venkat Sharma

                                         its duly authorized
                                         Chief Executive Officer


                                     Lot 4 LLC

                                     By: /s/ Robert D. Scinto
                                         --------------------
                                         Robert D. Scinto, a member
<PAGE>

State of Connecticut
                                 ss Town of Fairfield
County of Fairfield

     Personally appeared Venkat Sharma, signer and sealer of the foregoing
instrument and duly authorized President of Acorn Information Services, Inc.,
who acknowledged the same to be his free act and deed and duly authorized free
act and deed of Acorn Information Services, Inc., before me, this ________ day
of April, 1998.


                                     ___________________________________
                                     Commissioner of the Superior Court/
                                     Notary Public

State of Connecticut
                                 ss City of Shelton
County of Fairfield

     Personally appeared Robert D. Scinto, signer and sealer of the foregoing
instrument and the duly authorized member of Lot 4 LLC, who acknowledged the
same to be his free act and deed and the duly authorized free act and deed of
Lot 4 LLC before me, this 20th day of April, 1998.


                                     /s/ Eleanor M. Choate
                                     ---------------------
                                         Notary Public


                                     Eleanor M. Choate
                                     Notary Public
                                     My Commission Expires July 31, 1998
<PAGE>

                                    46-375



                           MONTHLY RENTAL BREAKDOWN



<TABLE>
<S>                                                            <C>
BASIC MINIMUM MONTHLY RENT                                     $ 7,166.00
BUDGETED MONTHLY OPERATING EXPENSES @ $5.52                    $ 3,296.36
BUDGETED INTERIOR ELECTRIC                                     $   746.45
OTHER CHARGES                                                  $   378.27
                                                               ----------

           TOTAL MONTHLY PAYMENT DUE JANUARY 1, 1999           $11,587.08
                                                               ----------
</TABLE>