Exhibit 4.3

SUPPLEMENTAL INDENTURE, (this “Supplemental Indenture”) dated as of May 22, 2015, by and among Blue Coat Holdings, Inc. (successor in interest to Batman Merger Sub, Inc.), a Delaware corporation (“Blue Coat”), the parties that are signatories hereto as Guarantors (each a “Guaranteeing Subsidiary”) and Wilmington Trust, National Association, as Trustee under the Indenture referred to below.

W I T N E S S E T H:

WHEREAS, each of Batman Merger Sub, Inc., a Delaware corporation (“Merger Sub”) and the Trustee have heretofore executed and delivered an indenture dated as of May 22, 2015 (as amended, supplemented, waived or otherwise modified, the “Indenture”), providing for the issuance of an aggregate principal amount of $470,000,000 of 8.375% Senior Notes due 2023 (the “Notes”) of the Issuer;

WHEREAS, the Indenture provides that Blue Coat and the Guaranteeing Subsidiaries shall execute and deliver to the Trustee a supplemental indenture pursuant to which Blue Coat shall assume, and the Guaranteeing Subsidiaries shall unconditionally guarantee, all of Merger Sub’s Obligations under the Notes and the Indenture on the terms and conditions set forth herein and under the Indenture (in the case of the Guaranteeing Subsidiary, the “Note Guarantee”), each on the terms and conditions set forth herein; and

WHEREAS, pursuant to Section 9.1 of the Indenture, the Issuer, any Guarantor and the Trustee are authorized to execute and deliver this Supplemental Indenture to amend or supplement the Indenture, without the consent of any Holder;

NOW, THEREFORE, in consideration of the foregoing and for other good and valuable consideration, the receipt of which is hereby acknowledged, Blue Coat, the Guaranteeing Subsidiaries and the Trustee mutually covenant and agree for the benefit of the Trustee and the Holders of the Notes as follows:

ARTICLE I

DEFINITIONS

SECTION 1.1. Defined Terms. As used in this Supplemental Indenture, terms defined in the Indenture or in the preamble or recitals hereto are used herein as therein defined. The words “herein,” “hereof” and “hereby” and other words of similar import used in this Supplemental Indenture refer to this Supplemental Indenture as a whole and not to any particular section hereof.

ARTICLE II

ASSUMPTION OF OBLIGATIONS; AGREEMENT TO BE BOUND; GUARANTEE

SECTION 2.1. Assumption of Obligations. Blue Coat hereby agrees to unconditionally assume Merger Sub’s Obligations, and hereby assumes Merger Sub’s Obligations, under the Indenture and the Notes on the terms and subject to the conditions set forth in the Indenture and to be bound by all other applicable provisions of the Indenture and the Notes and to perform all of the obligations and agreements of Merger Sub under the Indenture and the Notes.

SECTION 2.2. Agreement to be Bound. Each of the Guaranteeing Subsidiaries hereby becomes a party to the Indenture as a Guarantor and as such will have all of the rights and be subject to all of the obligations and agreements of a Guarantor under the Indenture.

SECTION 2.3. Guarantee. Each of the Guaranteeing Subsidiaries agrees, on a joint and several basis with all the existing Guarantors, to fully, unconditionally and irrevocably Guarantee to each Holder of the Notes and the Trustee the Guaranteed Obligations pursuant to Article X of the Indenture on a senior basis.

ARTICLE III

MISCELLANEOUS

SECTION 3.1. Notices. All notices and other communications to the Guarantors shall be given as provided in the Indenture.

SECTION 3.2. Merger and Consolidation. Each Guaranteeing Subsidiary shall not sell or otherwise dispose of all or substantially all of its assets to, or consolidate with or merge with or into, another Person (other than the Issuer or any Restricted Subsidiary that is a Guarantor or becomes a Guarantor concurrently with the transaction) except in accordance with Section 4.1(f) of the Indenture.

SECTION 3.3. Release of Guarantee. The Note Guarantees hereunder may be released in accordance with Section 10.2 of the Indenture.

SECTION 3.4. Parties. Nothing expressed or mentioned herein is intended or shall be construed to give any Person, firm or corporation, other than the Holders and the Trustee, any legal or equitable right, remedy or claim under or in respect of this Supplemental Indenture or the Indenture or any provision herein or therein contained.

SECTION 3.5. Governing Law. This Supplemental Indenture shall be governed by, and construed in accordance with, the laws of the State of New York.

SECTION 3.6. Severability. In case any provision in this Supplemental Indenture shall be invalid, illegal or unenforceable, the validity, legality and enforceability of the remaining provisions shall not in any way be affected or impaired thereby and such provision shall be ineffective only to the extent of such invalidity, illegality or unenforceability.

SECTION 3.7. Benefits Acknowledged. Each Guaranteeing Subsidiary’s Note Guarantee is subject to the terms and conditions set forth in the Indenture. Each Guaranteeing Subsidiary acknowledges that it will receive direct and indirect benefits from the financing arrangements contemplated by the Indenture and this Supplemental Indenture and that the guarantee and waivers made by it pursuant to its Note Guarantee are knowingly made in contemplation of such benefits.

SECTION 3.8. Ratification of Indenture; Supplemental Indentures Part of Indenture. Except as expressly amended hereby, the Indenture is in all respects ratified and confirmed and all the terms, conditions and provisions thereof shall remain in full force and effect. This Supplemental Indenture shall form a part of the Indenture for all purposes, and every Holder of Notes heretofore or hereafter authenticated and delivered shall be bound hereby.

SECTION 3.9. The Trustee. The Trustee makes no representation or warranty as to the validity or sufficiency of this Supplemental Indenture or with respect to the recitals contained herein, all of which recitals are made solely by the other parties hereto.

SECTION 3.10. Counterparts. The parties hereto 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. The exchange of copies of this Supplemental Indenture and of signature pages by facsimile or electronic transmission shall constitute effective execution and delivery of this Supplemental Indenture as to the parties hereto and may be used in lieu of the original Supplemental Indenture for all purposes. Signatures of the parties hereto transmitted by facsimile or electronic transmission shall be deemed to be their original signatures for all purposes.

SECTION 3.11. Execution and Delivery. Each Guaranteeing Subsidiary agrees that its Note Guarantee shall remain in full force and effect notwithstanding any failure to endorse on each Note a notation of any such Note Guarantee.

SECTION 3.12. Headings. The headings of the Articles and the Sections in this Supplemental Indenture are for convenience of reference only and shall not be deemed to alter or affect the meaning or interpretation of any provisions hereof.

SECTION 3.13. Jurisdiction. The parties hereto agree that any suit, action or proceeding arising out of or based upon this Supplemental Indenture may be instituted in any state or Federal court in the Borough of Manhattan, New York, New York, and any appellate court from any thereof, and each party hereto irrevocably submits to the non-exclusive jurisdiction of such courts in any suit, action or proceeding. The parties hereto irrevocably waive, to the fullest extent permitted by law, any objection to any suit, action, or proceeding that may be brought in connection with this Supplemental Indenture, including such actions, suits or proceedings relating to securities laws of the United States or any state thereof, in such courts whether on the grounds of venue, residence or domicile or on the ground that any such suit, action or proceeding has been brought in an inconvenient forum. The parties hereto agree that final judgment in any such suit, action or proceeding brought in such court shall be conclusive and binding upon them, and may be enforced in any court to the jurisdiction of which they are subject by a suit upon such judgment.

SECTION 3.14. Waiver of Jury Trial. THE PARTIES HERETO HEREBY IRREVOCABLY AND UNCONDITIONALLY WAIVE, TO THE FULLEST EXTENT PERMITTED BY APPLICABLE LAW, ANY AND ALL RIGHT TO TRIAL BY JURY IN ANY LEGAL ACTION OR PROCEEDING ARISING OUT OF OR RELATING TO THIS SUPPLEMENTAL INDENTURE AND FOR ANY COUNTERCLAIM THEREIN.

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

[Signature Page to Supplemental Indenture]

[Signature Page to Supplemental Indenture]