UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

FORM 12b-25

NOTIFICATION OF LATE FILING

(Check one):

o Form 10-K

o Form 20-F

o Form 11-K

o Form 10-Q

o Form 10-D

o Form N-SAR

o Form N-CSR

For Period Ended:

o Transition Report on Form 10-K

o Transition Report on Form 20-F

o Transition Report on Form 11-K

x Transition Report on Form 10-Q

o Transition Report on Form N-SAR

For the Transition Period Ended:

December 31, 2007

Read Instructions (on back page) Before Preparing Form. Please Print or Type.
Nothing in this form shall be construed to imply that the Commission has verified any information contained herein.

ACI Worldwide, Inc.

Full Name of Registrant                  

Transaction Systems Architects, Inc.

Former Name if Applicable            

120 Broadway, Suite 3350

Address of Principal Executive Office (Street and Number)

New York, New York 10271

City, State and Zip Code          

o

(a)

The reason described in reasonable detail in Part III of this form could not be eliminated without unreasonable effort or expense

x

(b)

The subject annual report, semi-annual report, transition report on Form 10-K, Form 20-F, Form 11-K, Form N-SAR or Form N-CSR, or portion thereof, will be filed on or before the fifteenth calendar day following the prescribed due date; or the subject quarterly report or transition report on Form 10-Q or subject distribution report on Form 10-D, or portion thereof, will be filed on or before the fifth calendar day following the prescribed due date; and

o

(c)

The accountant’s statement or other exhibit required by Rule 12b-25(c) has been attached if applicable.

(1)

Name and telephone number of person to contact in regard to this notification

Henry C. Lyons

(646)

348-6711

(Name)

(Area Code)

(Telephone Number)

(2)

Have all other periodic reports required under Section 13 or 15(d) of the Securities Exchange Act of 1934 or Section 30 of the Investment Company Act of 1940 during the preceding 12 months or for such shorter period that the registrant was required to file such report(s) been filed ? If answer is no, identify report(s).

x Yes    o No

(3)

Is it anticipated that any significant change in results of operations from the corresponding period for the last fiscal year will be reflected by the earnings statements to be included in the subject report or portion thereof?

o Yes    x No

If so, attach an explanation of the anticipated change, both narratively and quantitatively, and, if appropriate, state the reasons why a reasonable estimate of the results cannot be made.

Forward Looking Statements:  This Notification of Late Filing on Form 12b-25 regarding ACI Worldwide, Inc. contains forward-looking statements based on current expectations that involve a number of risks and uncertainties.  Generally, forward-looking statements do not relate strictly to historical or current facts and may include words or phrases such as the Company “believes,” “will,” “expects,” “looks forward to,” and words and phrases of similar impact.  The forward-looking statements are made pursuant to safe harbor provisions of the Private Securities Litigation Reform Act of 1995.  Forward-looking statements in this report include, but are not limited to, statements regarding the Company’s desired timing regarding the filing of its Transition Report on Form 10-Q.

Any or all of the forward-looking statements may turn out to be wrong.  They can be affected by the judgments and estimates underlying such assumptions or by known or unknown risks and uncertainties. These factors include, without limitation, the risk that additional information may arise from the preparation of the Company’s financial statements or other subsequent events that would require the Company to make adjustments to its financial statements.  Consequently, no forward-looking statement can be guaranteed.  In addition, the Company disclaims any obligation to update any forward-looking statements after the date of this report.

All of the foregoing forward-looking statements are expressly qualified by the risk factors discussed in the Company’s filings with the Securities and Exchange Commission.  For a detailed discussion of these risk factors, parties that are relying on the forward-looking statements should review the Company’s filings with the Securities and Exchange Commission, including the Company’s Form 10-Q filed on June 29, 2007, the Company’s Form 10-Q filed on August 10, 2007, the Company’s Form 10-Q filed on September 25, 2007, the Company’s Form 10-K filed January 30, 2008 and specifically the section entitled “Factors That May Affect the Company’s Future Results or the Market Price of the Company’s Common Stock.”

ACI WORLDWIDE, INC.

Date:       February 12, 2008   

By:

     /s/  Henry C. Lyons    

Name:     Henry C. Lyons

Title:       Chief Financial Officer, Senior Vice President and

                Treasurer

ATTENTION

Intentional misstatements or omissions of fact constitute Federal Criminal Violations (See 18 U.S.C. 1001).