Qualys, Inc. Offer Letter and Amendment for Chief Financial Officer Donald C. McCauley

Exhibit 10.6

February 7, 2006

Donald McCauley

[Address]

Dear Don:

On behalf of Qualys, Inc., I am pleased to offer you the position of Chief Financial Officer reporting to Philippe Courtot, Chairman and CEO. Your location of work will be Redwood City, CA. The details of your offer are outlined below.

Qualys, Inc.

1600 Bridge Parkway, Redwood Shores, CA 94065

###-###-#### F ###-###-#### www.qualys.com

As a QUALYS employee, you will be expected to abide by Company rules and regulations, and sign and comply with the attached Proprietary Information and Inventions Agreement, which prohibit unauthorized use or disclosure of QUALYS’ proprietary information.

Your employment relationship with QUALYS is at-will. You may terminate your employment with QUALYS at any time and for any reason whatsoever simply by notifying QUALYS. Likewise, QUALYS may terminate your employment at any time and for any reason whatsoever with or without cause or advance notice. This at-will employment relationship cannot be changed except in a writing signed by a Company officer.

This letter, together with your Employee Proprietary Information and Inventions Agreement and the option agreement between you and Qualys (relating to your option grant described above), forms the complete and exclusive statement of your employment agreement with QUALYS. The employment terms in this letter supersede any other agreements or promises made to you by anyone, whether oral or written. It is also contingent upon providing evidence of your legal right to work in the United States as required by the Immigration and Naturalization Service

We look forward to your acceptance of employment with QUALYS under the terms described above. To accept this offer, please sign and date this letter. Please return the original offer letter along with the Employee Proprietary Information and Inventions Agreement in the enclosed envelope and keep a copy of the offer letter for your records. This offer will expire on February 10th, 2006

Don, we are excited about you joining our team. If you have any questions, please feel free to call me at ###-###-####.

QUALYS, INC.

AMENDMENT TO OFFER LETTER

This amendment (the “Amendment”) is made by and between Donald McCauley (“Executive”) and Qualys, Inc., a Delaware corporation (the “Company” and together with the Executive hereinafter collectively referred to as the “Parties”) on September __, 2012.

WHEREAS, the Parties previously entered into an offer letter agreement dated February 7, 2006 (the “Agreement”);

WHEREAS, the Parties intend and expect that severance payments under the Agreement are exempt from Section 409A of the Internal Revenue Code of 1986, as amended (the “Code”) and the final regulations and guidance thereunder (“Section 409A”) under the separation pay plan exception set forth in Treasury Regulation Section 1.409A-1(b)(9)(iii) and/or the short-term deferral rule set forth in Treasury Regulation Section 1.409A-1(b)(4), as applicable; and

WHEREAS, in an abundance of caution, the Parties intend to clarify certain payment terms with respect to the timing of the release of claims so that, to the extent the severance payments become subject to Section 409A, the severance payments and benefits under the Agreement will comply with the requirements of Section 409A.

NOW, THEREFORE, in consideration of the foregoing and for other good and valuable consideration, Executive and the Company agree that the Agreement is hereby amended as follows:

1. Severance. The second paragraph of the section of the Agreement under the heading of “Salary:” is hereby amended and replaced as follows:

“Should you be terminated without cause, you will be entitled to a lump-sum cash severance payment equal to 6 months of base salary at your final rate of pay and you will also be entitled to 6 months of Company-paid COBRA coverage (if you timely elect COBRA coverage), in each case, provided that you sign the Qualys General Release of Claims (the “Release”) and that the Release becomes effective and irrevocable no later than sixty (60) days following your separation date (such deadline, the “Release Deadline”). If the Release does not become effective and irrevocable by the Release Deadline, you will forfeit any rights to severance or benefits under this letter. In no event will severance payments or benefits be paid or provided until the Release becomes effective and irrevocable.

Any severance payments or benefits that are Deferred Payments (as defined below) under this letter and, to the extent necessary to avoid imposition of additional tax or income recognition prior to actual payment under Section 409A of the Internal Revenue Code of 1986, as amended and the final regulations and official guidance thereunder (“Section 409A”), any other severance payments or benefits under this letter, will be paid on, or, in the case of installments, will not commence until, the sixtieth (60th) day following your separation from service, or, if later, such time as required by the section of this letter with the heading “Section 409A.” Any installment payments that would have been made to you during the sixty (60) day period immediately following your separation from service but for the preceding sentence will be paid to you on the sixtieth (60th) day following your separation from service and the remaining payments shall be made as provided in this letter.”

2. Section 409A. A new section is hereby added to the Agreement under the heading of Section 409A to read in its entirety as follows:

3. Full Force and Effect. To the extent not expressly amended hereby, the Agreement shall remain in full force and effect.

4. Entire Agreement. This Amendment and the Agreement constitute the full and entire understanding and agreement between the Parties with regard to the subjects hereof and thereof. This Amendment may be amended at any time only by mutual written agreement of the Parties.

5. Counterparts. This Amendment may be executed in counterparts, all of which together shall constitute one instrument, and each of which may be executed by less than all of the parties to this Amendment.

6. Governing Law. This Amendment will be governed by the laws of the State of California (with the exception of its conflict of laws provisions).

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IN WITNESS WHEREOF, each of the Parties has executed this Amendment, in the case of the Company by its duly authorized officer, as of the date set forth above.

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