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UNITED STATES

SECURITIES AND EXCHANGE COMMISSION

Washington, D.C. 20549

FORM 10-Q/A

(Amendment No. 1)

(Mark One)

OR

Commission file number 000-24389

VASCO Data Security International, Inc.

(Exact Name of Registrant as Specified in Its Charter)

1901 South Meyers Road, Suite 210

Oakbrook Terrace, Illinois 60181

(Address of Principal Executive Offices)(Zip Code)

(630) 932-8844

(Registrant’s telephone number, including area code)

Indicate by check mark whether the registrant (1) has filed all reports required to be filed by Section 13 or 15(d) of the Securities Exchange Act of 1934 during the preceding 12 months (or for such shorter period that the registrant was required to file such reports), and (2) has been subject to such filing requirements for the past 90 days.    x  Yes    ¨  No

Indicate by check mark whether the registrant has submitted electronically and posted on its corporate Web site, if any, every Interactive Data File required to be submitted and posted pursuant to Rule 405 of Regulation S-T (§232.405 of this chapter) during the preceding 12 months (or for such shorter period that the registrant was required to submit and post such files).    Yes  ¨    No  ¨

Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer or a smaller reporting company. See definition of “large accelerated filer,” “accelerated filer” and “smaller reporting company” in Rule 12b-2 of the Exchange Act.

Indicate by check mark whether the registrant is a shell company (as defined in Rule 12b-2 of the Exchange Act).    Yes  ¨    No  x

There were 38,043,306 shares of Common Stock, $.001 par value per share, outstanding at July 29, 2011.

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VASCO Data Security International, Inc.

Form 10-Q/A

For The Quarterly Period Ended June 30, 2011

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Explanatory Note

Vasco Data Security International, Inc. is filing this Amendment No. 1 (the “Form 10-Q/A”) to our Quarterly Report on Form 10-Q for the quarter ended June 30, 2011 (the “Form 10-Q”), filed with the U.S. Securities and Exchange Commission (“SEC”) on August 5, 2011, for the sole purpose of furnishing the Interactive Data File as Exhibit 101 in accordance with Rule 405(a)(2) of Regulation S-T.

No other changes have been made to the Form 10-Q. This Form 10-Q/A continues to speak as of the original filing date of the Form 10-Q, does not reflect events that may have occurred subsequent to the original filing date, and does not modify or update any related disclosures made in the Form 10-Q.

Exhibit 101 furnished herewith. In accordance with Rule 406T of Regulation S-T, the information in Exhibit 101 shall not be deemed to be “filed” for purposes of the Securities and Exchange Act of 1934, or otherwise subject to liability under this section, and shall not be incorporated by reference into any registration statement or other document filed under the Securities Act of 1933, as amended, except as expressly set forth by specific reference in such filing.

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PART II. OTHER INFORMATION

Item 6. Exhibits.

Exhibit 31.1 – Rule 13a-14(a)/15d-14(a) Certification of Principal Executive Officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002, dated August 5, 2011. (1)

Exhibit 31.2 – Rule 13a-14(a)/15d-14(a) Certification of Principal Financial Officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002, dated August 5, 2011. (1)

Exhibit 32.1 – Section 1350 Certification of Principal Executive Officer pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, dated August 5, 2011. (1)

Exhibit 32.2 – Section 1350 Certification of Principal Financial Officer pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, dated August 5, 2011. (1)

Exhibit 101.INS – XBDL Instance Document (2)

Exhibit 101.SCH – XBRL Taxonomy Extension Schema Document (2)

Exhibit 101.CAL – XBRL Taxonomy Extension Calculation Linkbase Document (2)

Exhibit 101.LAB – XBRL Taxonomy Extension Label Linkbase Document (2)

Exhibit 101.PRE – XBRL Taxonomy Extension Presentation Linkbase Document (2)

Exhibit 101.DEF – XBRL Taxonomy Extension Definition Linkbase Document (2)

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SIGNATURES

Pursuant to the requirements of the Securities Exchange Act of 1934, the Registrant has duly caused this Report to be signed on its behalf by the undersigned, thereunto duly authorized, on August 25, 2011.

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EXHIBIT INDEX

Exhibit 31.1 – Rule 13a-14(a)/15d-14(a) Certification of Principal Executive Officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002, dated August 5, 2011. (1)

Exhibit 31.2 – Rule 13a-14(a)/15d-14(a) Certification of Principal Financial Officer pursuant to Section 302 of the Sarbanes-Oxley Act of 2002, dated August 5, 2011. (1)

Exhibit 32.1 – Section 1350 Certification of Principal Executive Officer pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, dated August 5, 2011. (1)

Exhibit 32.2 – Section 1350 Certification of Principal Financial Officer pursuant to Section 906 of the Sarbanes-Oxley Act of 2002, dated August 5, 2011. (1)

Exhibit 101.INS – XBRL Instance Document (2)

Exhibit 101.SCH – XBRL Taxonomy Extension Schema Document (2)

Exhibit 101.CAL – XBRL Taxonomy Extension Calculation Linkbase Document (2)

Exhibit 101.LAB – XBRL Taxonomy Extension Label Linkbase Document (2)

Exhibit 101.PRE – XBRL Taxonomy Extension Presentation Linkbase Document (2)

Exhibit 101.DEF – XBRL Taxonomy Extension Definition Linkbase Document (2)

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