<PAGE>

                                                                   Exhibit 10.12

                            SECOND AMENDMENT TO LEASE

      WHEREAS, Monarch Life Insurance Company (hereinafter referred to as the
"Original Landlord") and SS&C TECHNOLOGIES, INC. (hereinafter referred to as the
"Tenant" or the "Lessee") entered into a certain lease for approximately 48,126
square feet of rentable area on the first and second floors (hereinafter
referred to as the "Premises") of the building known and numbered as 80
Lamberton Road, Windsor, Connecticut (hereinafter referred to as "Building")
dated September 23, 1997, as amended by a certain First Amendment to Lease dated
November 18, 1997, whereby the Premises were expanded to consist of a total of
54,082 square feet of rentable area on the first and second floors and the
"Highbay I Space", (hereinafter referred to as the "Initial Lease" and the
"First Amendment", respectively, and collectively referred to as the "Lease");
and

      WHEREAS, NEW BOSTON LAMBERTON LIMITED PARTNERSHIP (hereinafter referred to
as the "Landlord" or the "Lessor") is the successor in interest to the Original
Landlord; and

      WHEREAS, Tenant desires to lease additional space at the Building; and

      WHEREAS, Landlord and Tenant now mutually desire to establish the terms
and conditions for the rental of additional space at the Building, and to amend
the Lease in various respects as more particularly set forth below.

      NOW THEREFORE, in consideration of the mutual covenants herein contained
and for other good and valuable consideration, the receipt and sufficiency of
which are hereby acknowledged by both parties hereto, Landlord and Tenant hereby
agree to amend the Lease as follows:

      1. Section 2 (a) of the Lease is amended by inserting the following
language after the first sentence of the first paragraph thereof:

      "Effective as of July 1, 1999, the Premises shall include approximately an
      additional 19,663 square feet of net rentable area; consisting of
      approximately an additional 7,300 square feet of net rentable area (the
      exact dimensions of which are to be determined at a later date, and will
      be incorporated into a revised Third Amendment to Lease in substantially
      the same form as this Second Amendment to Lease), and an additional 12,363
      square feet of net rentable area on the ground floor of the Building
      (hereinafter referred to as the "Highbay II Space", and the "Ground Floor
      Space", respectively, and collectively hereinafter referred to as the
      "Second Amendment Expansion Space") as more particularly shown as the
      cross-hatched area on Exhibit A-2 attached hereto and incorporated herein
      by reference."

      2. Section 2 of the Lease is amended by inserting the following language
after subsection (c) thereof:

      "(d) Tenant shall have the right, without payment of rent or charge, to
      use space in the Lamberton Road side of the Building (the "Lobby") for its
      reception area as set forth in Exhibit A-3 attached hereto and
      incorporated hereby. Tenant, at its sole cost and expense
<PAGE>
      shall make the improvements to the Lobby (the "Lobby Improvements"), as
      set forth in Exhibit E attached hereto and incorporated hereby, upon
      Landlord's written approval of the same, which approval shall not be
      unreasonably withheld or delayed. The Lobby Improvements will not
      interfere with the means of ingress or egress for other tenants in the
      Building, or interfere with any Building systems. Upon the completion of
      the Lobby Improvements, Tenant will, at its sole cost, provide all
      cleaning services to the Lobby in accordance with prior Building
      practices, and the standards of a first class office building. Upon the
      termination or expiration of the Lease, Tenant will surrender the Lobby in
      broom clean condition, and in good order and repair, reasonable wear and
      tear excepted."

      3. Section 3 (c) of the Lease is amended by inserting the following
language at the end thereof.

      "Notwithstanding anything to the contrary herein, Tenant's right to extend
      this Lease in accordance with this Section 3 (c) shall not include a right
      to extend this Lease with respect to the Ground Floor Space."

      4. Section 4 (a) of the Lease is amended by inserting the following
language after Section 4(a) (ii):

      "(iii) In addition to the Minimum Annual Rent set forth in Section 4 (a)
      (i) and (ii), Tenant shall pay rent with respect to the Highbay II Space
      as set forth below;

<TABLE>
<CAPTION>
PERIOD               RENT PER SQ. FT.     MONTHLY RENT
------               ----------------     ------------
<S>                  <C>                  <C>
7/1/99-7/31/99       NONE                 NONE
8/1/99-12/31/02      $13.25               to be determined upon re-
1/1/03-1/14/08       $14.00               measurement at a later date.
</TABLE>

      In addition to the Minimum Annual Rent set forth in Section 4 (a) (i) and
(ii), Tenant shall pay rent with respect to the Ground Floor Space as set forth
below;

<TABLE>
<CAPTION>
PERIOD               RENT PER SQ. FT.     MONTHLY RENT
------               ----------------     ------------
<S>                  <C>                  <C>
7/1/99-7/31/99       N/A                      $6,196.19
8/1/99-6/30/01       $14.75                  $15,196.19
7/1/01-6/30/03       $15.25                  $15,711.31
7/1/03-6/30/05       $15.75                  $16,226.44
7/1/05-1/14/08       $16.25                  $16,741.56"
</TABLE>

      5. Section 5 (a) of the Lease is amended by inserting the following
language after the second sentence of the first paragraph thereof"

      "Effective as of the July 1, 1999, the "Lessee's Proportionate Share" for
      purposes of this Section 5 (a) shall be approximately 46.8% (the exact
      "Lessee's Proportionate Share" shall be determined at a later date upon
      re-measurement by Landlord and will be incorporated into a revised Third
      Amendment to Lease in substantially the same form as this Second Amendment
      to Lease)".


                                      -2-
<PAGE>
      6. Section 7 of the Lease is amended by inserting the following subsection
at the end thereof:

      "(e) Effective July 1, 1999, thee Lessee accepts the Premises (with the
      exception of the Highbay II Space and Ground Floor Space) in its "As Is"
      condition and acknowledges the satisfactory completion of all improvements
      and conditions set forth in Section 7 (a) - (d). Tenant shall do the work
      shown as the work to be performed by Tenant on, and in accordance with,
      final plans and specifications prepared by Tenant's Architect, and to be
      reviewed and approved by Landlord (hereinafter referred to as "Build-Out
      Drawings" a copy of which shall be attached hereto and incorporated hereby
      as Exhibit A-4), which Build-Out Drawings will be prepared at Tenant's
      expense. The work shown thereon as the work to be performed by Tenant
      shall be done in a good and workmanlike manner, in accordance with all
      laws, rules, regulations and ordinances applicable thereto, and pursuant
      to a Town of Windsor Building Permit (hereinafter referred to as "Tenant's
      Work"), and shall be done by Tenant's choice of contractor (which shall be
      subject to Landlord's reasonable approval) pursuant to a Stipulated Sum
      AIA Document A101 Standard Form of Agreement Between Tenant and Contractor
      (hereinafter referred to as "General Contractor"). Tenant shall have no
      authority to make any changes to the Build-Out Drawings after approval of
      the same by Landlord and Tenant, whether by change order or otherwise,
      absent Landlord's prior written consent, which consent shall not be
      unreasonably withheld or delayed. Tenant's Work shall be done at Tenant's
      expense except as otherwise provided herein. Tenant shall pursue the
      issuance of a permanent Certificate of Occupancy for Tenant's Work after
      the completion of the same.

      Prior to the commencement of Tenant's Work, Tenant shall provide Landlord
with the General Contractor's firm quote for the cost of performing Tenant's
Work. Landlord shall provide an allowance of up to Two Hundred Thirty Nine
Thousand One Hundred Thirty Dollars ($239,130.00) towards the actual cost of
Tenant's Work (approximately One Hundred Fifteen Thousand Five Hundred Dollars
($115,500.00) towards the actual costs of performing Tenant's Work to the
Highbay II Space, and approximately One Hundred Twenty Three Thousand Six
Hundred Thirty Dollars ($123,630.00) toward the actual cost of performing
Tenant's Work on the Ground Floor Space) (hereinafter collectively referred to
as the "TI Contribution"). Landlord shall pay to Tenant the TI Contribution
upon: the completion of Tenant's Work, the issuance of a Certificate of
Occupancy by the Town of Windsor, and Landlord's receipt of a lien waiver from
the General Contractor. The costs of performing Tenant's Work in excess of said
Two Hundred Thirty Nine Thousand One Hundred Thirty Dollars ($239,130.00) shall
be borne by Tenant.

      Tenant shall furnish and install any and all necessary trade fixtures,
equipment and other items necessary for the proper conduct of Tenant's business.
In no event shall Landlord be required to provide or install any trade fixtures
or equipment.

      Tenant agrees to employ for any work it may do pursuant to this Section 5
one or more responsible contractors whose labor will work in harmony with other
labor working in the Building and with suppliers of materials for use in
construction in and on the Building, and especially Tenant agrees that it will
not do or permit to be done anything which would cause any labor difficulty in
connection with any construction in the Building,


                                      -3-
<PAGE>
      Tenant shall require all such contractors employed by Tenant to carry
Worker's Compensation Insurance in accordance with statutory requirements and to
carry Commercial General Liability Insurance and Automobile Liability Insurance
covering such contractors in or about the Building and property in amounts not
less that Two Million ($2,000,000) Dollars combined single limits for property
damage, for injury or death of more than one person in a single accident and to
submit certificates of insurance evidencing such coverage to Landlord prior to
commencement of such work. Tenant agrees to indemnify and hold harmless Landlord
from all claims, actions, demands and causes of actions occasioned by Tenant's
contractors being on or about the Premises or the Building, and from Tenant's
contractors performing work in the Building or on the Premises.

      All contractors, subcontractors, mechanics, laborers, materialmen, and
others who perform any work, labor or services, or furnish any materials, or
otherwise participate in the labor or services, or furnish any materials, or
otherwise participate in the improvement of the Building shall be and are hereby
given notice that Tenant is not authorized to subject Landlord's interest in the
Building to any claim for mechanics', laborers' and materialmen's liens, and all
persons dealing directly or indirectly with Tenant may not look to the Building
as security for payment. Tenant shall save Landlord harmless from and against
all expenses, liens, claims or damages to either property or person which may or
might arise by reason of the making of any such additions, improvements,
alterations and/or installations.

      Tenant shall be liable to Landlord for any damage to the Building caused
by Tenant's work hereunder."

      7. Section 31 of the Lease is amended to provide that:

      "All notices required to be sent to the Lessor pursuant to the Lease shall
      be sent to the following addresses:

      To Lessor:          New Boston Lamberton, LP
                          c\o New Boston Fund, Inc.
                          One Longfellow Place, Suite 3612
                          Boston, MA 02114
                          Attn. Jerome L. Rappaport, Jr.

      With a copy to:     Rappaport, Aserkoff & Rappaport
                          One Longfellow Place, Suite 3611
                          Boston, MA 02114
                          Attn. Janet F. Aserkoff, Esq."

      8. Section 32 of the Lease is amended by adding the following sentence
after the first sentence of the first paragraph:

      "Lessor and Lessee warrant and represent to each other that they have
dealt with no broker or other person or entity entitled to a commission with
respect to the Second Amendment Expansion Space except Corporate Facility
Advisors and CB Richard Ellis - N.E. Partners, LP".

      9. Section 35 of the Lease is hereby deleted in its entirety.


                                      -4-
<PAGE>
      10. Notwithstanding anything to the contrary in the Lease, Tenant shall
have the right to install its own exclusive signage within the Lamberton Road
Building lobby entrance, consistent with a first class office building and
similar in design and materials to Tenant's existing signage, subject to
obtaining the Landlord's prior written consent after Landlord's review of the
planned signage, which consent shall not be unreasonably withheld or delayed.
All costs associated with said signage (including without limitation all
permitting costs) shall be at the Tenant's sole expense.

      11. Provided Tenant is not in default of its obligations hereunder, beyond
any applicable cure period, and subject to a right of first refusal in favor of
Milliman & Robertson, as presently exists under its lease, Landlord shall
provide Tenant with written notice (the "Right of First Offer Notice") for the
approximately 11,147 square feet of rentable area on the second floor of the
I-91 side of the Building should said space become available for lease.
Landlord's Right of First Offer Notice to Tenant shall set forth the premises'
square footage, the availability date, the term of occupancy (which term shall
be coterminous with the term of this lease as it may be extended), the rent, the
base years for the purpose of Tax and Operating Cost Excess, and the tenant
improvements to be performed by Landlord, if any. The terms and conditions
contained in the Right of First Offer Notice shall reflect Landlord's good faith
determination of the then current fair market rental terms available for
comparable premises in the Building to new tenants. Tenant shall have fifteen
(15) days following receipt of the Right of First Offer Notice to accept said
space on the terms and conditions offered, and if Tenant shall fail to accept
the Offer within said fifteen (15) day period, Tenant shall have waived its
right to the space and shall have no further right pursuant to this Section 11
to the space offered for the remainder of the term of this Lease, as it may be
extended. In the event Tenant accepts the offer of any space pursuant to this
Section 11, Landlord and Tenant shall execute an amendment to this lease,
setting forth the terms and conditions for the lease by Tenant of the space so
acquired.

      12. Except as herein provided, all other terms and conditions of the Lease
are hereby ratified and confirmed, and shall remain in full force and effect.


             THE REMAINDER OF THIS PAGE IS INTENTIONALLY LEFT BLANK.
                      SIGNATURES ARE ON THE FOLLOWING PAGE.


                                      -5-
<PAGE>
      IN WITNESS WHEREOF, Landlord and Tenant have caused this Second Amendment
to Lease to be duly executed, under seal, by persons hereunto duly authorized,
in multiple counterparts, each of which shall be considered an original hereof,
as of this ____ day of April 1999.

                                        LANDLORD:
                                        NEW BOSTON LAMBERTON LIMITED PARTNERSHIP
                                        BY: NEW BOSTON FUND IV, INC.
                                        Its General Partner


/s/ illegible                           By: /s/ Jerome L. Rappaport, Jr.
---------------------                       ------------------------------------
Witness                                 Jerome L. Rappaport, Jr.
                                        Its President

                                        TENANT:

                                        SS&C TECHNOLOGIES, INC.

/s/ illegible                           By: /s/ Anthony R. Guarascio
---------------------                       ------------------------------------
Witness                                 Anthony R. Guarascio
                                        Its Senior Vice President, Finance and
                                             Chief Financial Officer



                                      -6-