FOURTH SUPPLEMENTAL INDENTURE

Exhibit 4.3

FOURTH SUPPLEMENTAL INDENTURE

FOURTH SUPPLEMENTAL INDENTURE (this “Supplemental Indenture”), dated as of May 10, 2012, by and among CDW LLC, an Illinois limited liability company (the “Company”), CDW Finance Corporation, a Delaware corporation (“FinanceCo” and together with the Company, the “Issuers”), CDW Corporation, a Delaware corporation, and the subsidiaries of the Company party hereto (collectively, the “Guarantors”), and U.S. Bank National Association, as trustee (the “Trustee”), under the Indenture referred to below.

W I T N E S S E T H

WHEREAS, CDW Escrow Corporation, a Delaware corporation (the “Original Escrow Issuer”), and the Trustee executed and delivered an indenture dated as of April 13, 2011, as amended by the first supplemental indenture dated as of April 13, 2011, among the Original Escrow Issuer, the Issuers, the Guarantors and the Trustee, as further amended by the second supplemental indenture dated as of May 20, 2011, among CDW Escrow Corporation, a Delaware corporation, the Issuers, the Guarantors and the Trustee, and as further amended by the third supplemental indenture dated as of February 17, 2012, among the Issuers, the Guarantors and the Trustee (as so supplemented, the “Indenture”), providing for the issuance of 8.5% Senior Notes due 2019 (the “Notes”); and

WHEREAS, pursuant to Section 9.01 of the Indenture, the Trustee, the Issuers and the Guarantors are authorized to execute and deliver this Supplemental Indenture without the consent of the Holders of the Notes.

NOW, THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt and sufficiency of which is hereby acknowledged, the Issuers, the Guarantors and the Trustee mutually covenant and agree for the equal and ratable benefit of the Holders of the Notes as follows:

ARTICLE I

CAPITALIZED TERMS

Section 1.1 All capitalized terms which are used herein and not otherwise defined herein are defined in the Indenture and are used herein with the same meanings as in the Indenture.

ARTICLE II

AMENDMENTS TO INDENTURE

The Indenture is hereby amended effective as of the New Issue Date (as defined below) in accordance with this Article II; provided, however, that the amendments pursuant to Sections 2.1(a)(iv), 2.1(a)(v), 2.2(d) and 2.2(e) herein shall be considered effective as of the Issue Date. Except as so amended, the Indenture shall continue in full force and effect.

Section 2.1 AMENDMENTS TO DEFINITIONS.

(a) The following definitions are added to Section 1.01 of the Indenture in appropriate alphabetical order.

(i) “New Issue Date” means May 20, 2011.

(ii) “New Release Date” has the meaning set forth under Section 4.22.

(iii) “Original Release Date” means April 13, 2011, the date on which the escrow proceeds from the sale of the Initial Notes were released by the Escrow Agent.

(iv) “Subsidiary Guarantee” means any guarantee of the obligations of CDW under this Indenture and the Notes by a Subsidiary Guarantor in accordance with the provisions of this Indenture.

(v) “Subsidiary Guarantors” means each of:

(1) the Domestic Subsidiaries of CDW that is a Restricted Subsidiary and a guarantor under the Senior Secured Term Loan as of the Original Release Date; and

(2) any other Subsidiary of CDW that executes a Guarantee in accordance with the provisions of this Indenture.

(b) The definition of “Release Date” is hereby deleted in its entirety.

(c) Each reference to the term “Release Date” in the definitions of “Code,” “Fixed Charges,” “GAAP,” “Guarantor,” “Investments,” “Permitted Business,” “Permitted Investments,” “Permitted Liens,” “Senior Indebtedness,” and “Significant Subsidiary” in Section 1.01 of the Indenture is replaced with the term “Original Release Date.”

Section 2.2 AMENDMENTS TO ARTICLES.

(a) Each reference to the term “Release Date” in Sections 3.07, 4.03, 4.07, 4.08, 4.09, 4.10, 4.11, 4.12, 4.14, 4.15, 4.16, 4.17, 4.19, 5.01, 10.01 and 10.08 is replaced with the term “Original Release Date.”

(b) Each reference to the term “Release Date” in Sections 4.20, 4.21 and 4.22 is replaced with the term “New Release Date.”

(c) Each reference to the term “Issue Date” in Sections 4.21 and 4.22 is replaced with the term “New Issue Date.”

(d) Each reference to the term “Guarantor” in Section 10.08 of the Indenture is replaced with the term “Subsidiary Guarantor” and each reference to the term “Guarantee” in that Section is replaced with “Subsidiary Guarantee.”

(e) The reference to “subsidiary” in Section 10.08(1)(a) of the Indenture is deleted (the reference becomes duplicative as a result of the amendment to the Indenture made pursuant to Section 2.2(d) herein).

ARTICLE III

MISCELLANEOUS

Section 3.1 GOVERNING LAW. THIS SUPPLEMENTAL INDENTURE SHALL BE GOVERNED AND CONSTRUED IN ACCORDANCE WITH THE LAWS OF THE STATE OF NEW YORK, WITHOUT GIVING EFFECT TO ANY CONFLICT OF LAW PRINCIPLES.

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Section 3.2 INSTRUMENTS TO BE READ TOGETHER. This Supplemental Indenture is an indenture supplemental to and in implementation of the Indenture, and said Indenture and this Supplemental Indenture shall henceforth be read together.

Section 3.3 CONFIRMATION. The Indenture as amended and supplemented by this Supplemental Indenture is in all respects confirmed and preserved.

Section 3.4 COUNTERPARTS. The parties may sign any number of copies of this Supplemental Indenture. Each signed copy shall be an original, but all of them together represent the same agreement.

Section 3.5 EFFECT OF HEADINGS. The Section headings herein are for convenience only and shall not affect the construction hereof.

Section 3.6 THE TRUSTEE. The Trustee shall not be responsible in any manner whatsoever for or in respect of the validity or sufficiency of this Supplemental Indenture or for or in respect of the recitals contained herein, all of which recitals are made solely by the Issuers and the Guarantors.

[Signatures Pages Follow]

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IN WITNESS WHEREOF, the parties hereto have caused this Fourth Supplemental Indenture to be duly executed and attested, all as of the date first above written.