PURCHASE AGREEMENT



 Exhibit 4.2 
 $100,000,000 
 NETSCOUT SYSTEMS, INC. 
 Senior Secured Floating Rate Notes due 2012 
 Purchase Agreement 
 November 1, 2007 
 Integral Capital
Partners VI, L.P. 
 3000 Sand Hill Road 
 Building 3, Suite 240

 Menlo Park, California 94025 
 Silver Lake Partners, L.P.

 Silver Lake Investors, L.P. 
 Silver Lake Technology Investors,
L.L.C. 
 2775 Sand Hill Road, Suite 100 
 Menlo Park, California
94025 
 T3 Starburst II, LLC 
 TPG Starburst III, LLC 
 TPG
Starburst IV, LLC 
 301 Commerce Street 
 Suite 3300 

Fort Worth, Texas 76102 
 Ladies and Gentlemen: 
 NetScout Systems, Inc., a Delaware corporation (the “Company”), proposes to issue and sell to the several purchasers listed in Schedule 1
hereto (the “Purchasers”), $100,000,000 principal amount of its Senior Secured Floating Rates Notes due 2012 (the “Securities”). The Securities will be issued pursuant to an Indenture to be dated as of
November 1, 2007 (the “Indenture”) among the Company, the NetScout Guarantors listed in Schedule 2 hereto (the “NetScout Guarantors”), the NetGen Guarantors listed on Schedule 2 hereto (the “NetGen
Guarantors”, and together with the NetScout Guarantors, the “Guarantors”), and Wells Fargo Bank, National Association, as trustee (the “Trustee”), and will be guaranteed on a senior secured basis by each of
the Guarantors (the “Guarantees”). 
 The Securities will be sold to the Purchasers on a private placement basis pursuant to
an exemption under Section 4(2) and Regulation D (“Regulation D”) of the Securities Act of 1933, as amended (the “Securities Act”). 
 Holders of the Securities (including the Purchasers and their direct and indirect transferees) will be entitled to the benefits of a Registration Rights
Agreement (the “Registration Rights Agreement”), pursuant to which the Company and the Guarantors will agree to file one or more registration statements with the Securities and Exchange Commission (the “Commission”)
providing for the registration under the Securities Act of the Securities. 







 The Securities and the Guarantees will be secured by first priority liens, subject to permitted liens, on
substantially all of the tangible and intangible assets of the Company and the Guarantors, now owned or hereafter acquired by the Company and any Guarantor, other than accounts receivable and all proceeds therefrom and leased real property and
subject to certain other exceptions described in the Security Agreement (as defined below) (the “Collateral”). The Collateral shall be described in the Security Agreement to be dated as of the Closing Date (the “Security
Agreement”) to be delivered to Wells Fargo Bank, National Association, as collateral agent (the “Collateral Agent”), granting a first-priority security interest, with respect to the Collateral, subject to permitted liens,
for the benefit of the Collateral Agent and each holder of the Securities and the successors and assigns of the foregoing. 
 The Company
hereby confirms its agreement with the several Purchasers concerning the purchase and resale of the Securities, as follows: 
 1. Purchase
and Sale of the Securities. (a) On the basis of the representations, warranties and agreements set forth herein and subject to the conditions set forth herein, the Company agrees to issue and sell the Securities to the several Purchasers as
provided in this Agreement, and each Purchaser agrees, severally and not jointly, to purchase from the Company the respective principal amount of Securities set forth opposite such Purchaser’s name in Schedule 1 hereto at a price equal to 100%
of the principal amount thereof. The Company will not be obligated to deliver any of the Securities except upon payment for all the Securities to be purchased as provided herein. 
 (b) Each Purchaser, severally and not jointly, represents, warrants and agrees that: 
 (i) it has not solicited offers for, or offered or sold, and will not solicit offers for, or offer or sell, the Securities by means of any
form of general solicitation or general advertising within the meaning of Rule 502(c) of Regulation D or in any manner involving a public offering within the meaning of Section 4(2) of the Securities Act; 
 (ii) it has not solicited offers for, or offered or sold, and will not solicit offers for, or offer or sell, the Securities as part of the
offering; 
 (iii) it is acquiring the Securities for its own account for investment only and not with a view towards, or for
resale in connection with, the public sale or distribution thereof; provided, however, that by making the representations herein, it does not agree to hold any of the Securities for any minimum or other specific term and reserves the
right to dispose of the Securities at any time; provided, further, that it agrees that such disposition shall be in accordance with or pursuant to a registration statement or an exemption under the Securities Act. Such Purchaser is not a registered
broker-dealer. Such Purchaser is purchasing the Securities in the ordinary course of business, and has no agreement or understanding, directly or indirectly, with any person to distribute the Securities; 
  

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 (iv) it is an “accredited investor” as that term is defined in Rule 501(a) of
Regulation D as of the date of this Agreement and was not organized for the specific purpose of acquiring the Securities; 
 (v) it understands that the Securities are being offered and sold to it in reliance on specific exemptions from the registration requirements of the United States federal and state securities laws and that the Company is relying upon the
truth and accuracy of, and such Purchaser’s compliance with, the representations, warranties, covenants, agreements, acknowledgments and understandings of such Purchaser set forth herein in order to determine the availability of such exemptions
and the eligibility of such Purchaser to acquire the Securities; 
 (vi) it acknowledges that it (A) has been furnished
with or has had full access to all of the information that it considers necessary or appropriate for deciding whether to purchase the Securities, (B) has had an opportunity to ask questions and receive answers from the Company regarding the
terms and conditions of the offering, (C) has had access to information about the Company and its financial condition, results of operations, business, properties, management and prospects sufficient to enable it to evaluate its investment,
(D) can bear the economic risk of a total loss of its investment in the Securities and (E) has such knowledge and experience in business and financial matters so as to enable it to understand the risks of and form an investment decision
with respect to its investment in the Securities. Neither such inquiries nor any other due diligence investigations conducted by such Purchaser or its advisors, if any, or its representatives shall limit, modify, amend or affect the Company’s
representations and warranties contained in this Agreement and such Purchaser’s right to rely thereon; 
 (vii) it
understands that no United States federal or state agency or any other government or governmental agency has passed on or made any recommendation or endorsement of the Securities or the fairness or suitability of the investment in the Securities nor
have such authorities passed upon or endorsed the merits of the offering of the Securities; 
 (viii) it understands that the
Securities shall constitute “restricted securities” under Rule 144 of the Securities Act. Such Purchaser also understands that, except as provided in the Registration Rights Agreement, the Securities have not been and will not be
registered under the Securities Act or any state securities laws, and may not be offered for sale, sold, assigned or transferred without registration under the Securities Act or an exemption therefrom and that, in the absence of an effective
registration statement under the Securities Act, such Securities may only be sold under certain circumstances as set forth in the Securities Act. In that connection, such Purchaser is aware of Rule 144 and Rule 144A under the Securities Act and the
restrictions imposed thereby; 
 (ix) it is an entity duly organized, validly existing and in good standing under the laws of
the jurisdiction of its organization with the requisite power and authority to enter into and to consummate the transactions contemplated by this Agreement and the other Transaction Documents (as defined below) to which it is a party and otherwise
to carry out its obligations hereunder and thereunder. The execution, delivery and performance by such Purchaser of the transactions contemplated by this Agreement and 

  

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the other Transaction Documents to which it is a party have been duly authorized by all necessary corporate action on the part of such Purchaser. This
Agreement and the other Transaction Documents to which it is a party have been duly executed by such Purchaser, and when delivered by such Purchaser in accordance with the terms hereof and thereof, will constitute the valid and legally binding
obligations of such Purchaser, enforceable against it in accordance with their terms, except as enforceability may be limited by (i) applicable bankruptcy, reorganization, moratorium, fraudulent transfer, insolvency or other similar laws
affecting the enforcement of creditors’ rights generally, (ii) equitable principles relating to enforceability or (iii) any implied covenant of good faith and fair dealing (collectively, the “Enforceability
Exceptions”), and except that the rights to indemnity and contribution thereunder may be limited by applicable law and public policy; 
 (x) the office or offices of such Purchaser in which its investment decision was made is located at the address of such Purchaser set forth under Section 11 hereof; 
 (xi) the execution and performance of this Agreement and the other Transaction Documents to which it is a party do not conflict with any
agreement to which such Purchaser is a party or is bound thereby, any court order or judgment addressed to such Purchaser, or the constituent documents of the Purchaser except for such conflicts which would not, individually or in the aggregate,
have a material adverse effect on such Purchaser’s authority or ability to perform its obligations under this Agreement; 
 (xii) it is not purchasing the Securities as a result of any advertisement, article, notice or other communication regarding the Securities published in any newspaper, magazine or similar media or broadcast over television or radio or
presented at any seminar or any other general solicitation or general advertisement; and 
 (xiii) it, together with the other
Purchasers, currently hold an aggregate of $98,500,000 of outstanding principal amount of indebtedness of Network General Corporation pursuant to the Credit Agreement, dated as of July 16, 2004 and as subsequently amended, between Network
General Corporation and the Purchasers. 
 (c) Each Purchaser acknowledges and agrees that the Company and, for purposes of the opinion to be
delivered to the Purchasers pursuant to Sections 6(c), counsel for the Company, may rely upon the accuracy of the representations and warranties of the Purchasers, and compliance by the Purchasers with their agreements, contained in paragraph
(b) above, and each Purchaser hereby consents to such reliance. 
 (d) The Company and the Guarantors acknowledge and agree that the
Purchasers are acting solely in the capacity of an arm’s length contractual counterparty to the Company and the Guarantors with respect to the offering of Securities contemplated hereby (including in connection with determining the terms of the
offering) and not as financial advisors or fiduciaries to, or agents of, the Company, the Guarantors or any other person. Additionally, none of the Purchasers are advising the Company, the Guarantors or any other person as to any legal, tax,
investment, accounting or regulatory matters in any jurisdiction. The Company and the Guarantors shall consult with their own advisors concerning such matters and shall be responsible for making their own independent investigation and appraisal of
the transactions contemplated hereby, and none of the Purchasers shall have any responsibility or liability to the 

  

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Company or the Guarantors with respect thereto. Any review by the Purchasers of the Company, the Guarantors, and the transactions contemplated hereby or
other matters relating to such transactions will be performed solely for the benefit of such Purchasers and shall not be on behalf of the Company, the Guarantors or any other person. 
 2. Payment and Delivery. (a) Payment for and delivery of the Securities will be made at the offices of Simpson Thacher & Bartlett
LLP at 9:00 A.M., New York City time, on the date that the Closing (as defined in the Merger Agreement) occurs pursuant to the Agreement and Plan of Merger, dated as of September 19, 2007 (as amended on October 1, 2007 and October 11,
2007 and from time to time thereafter, the “Merger Agreement”), among the Company, Bradley Merger Sub LLC, Network General Central Corporation (“NetGen”), Network General Corporation (“NetGen
Opco”), and Silver Lake Partners, L.P. and TPG Starburst IV, LLC, in each case solely in its capacity as the representative for the stockholders of NetGen, or at such other time or place on the same or such other date, as the Purchasers and
the Company may agree upon in writing. The time and date of such payment and delivery is referred to herein as the “Closing Date”. 
 (b) Payment for the Securities shall be made by (i) the cancellation, severally and not jointly, by the Purchasers of all outstanding principal and accrued interest and premiums through the Closing Date listed in Schedule 3 hereto (the
“NetGen Indebtedness”) and owed by NetGen Opco to such Purchaser pursuant to the Credit Agreement, dated as of July 16, 2004 (as amended, the “NetGen Credit Agreement”), among NetGen, NetGen Opco, the
Subsidiary Guarantors identified therein and the Purchasers and (ii) the assignment, severally and not jointly, by the Purchasers of the portions listed in Schedule 3 hereto of the Total Cash Consideration (as defined in the Merger Agreement)
to be received by the Purchasers in the Merger (as defined in the Merger Agreement) in respect of the shares of NetGen Stock (as defined in the Merger Agreement) owned by the Purchasers immediately prior to the Merger, against delivery to the
Purchasers at the Closing of notes representing the Securities, with any transfer taxes payable in connection with the sale of the Securities duly paid by the Company. 
 3. Representations and Warranties of the Company and the Guarantors. Except as set forth on a Schedule of Exceptions delivered by the Company and the Guarantors to the Purchasers on the date hereof, the Company
and the Guarantors jointly and severally represent and warrant to each Purchaser that: 
 (a) Organization and Good Standing. The
Company and each of its subsidiaries (other than Network General Central Corporation and its subsidiaries) have been duly organized, and, to the knowledge of the Company and the NetScout Guarantors based solely on the information made available to
the Company and the NetScout Guarantors by Network General Central Corporation and its subsidiaries, Network General Central Corporation and its subsidiaries have been duly organized, and the Company and each of its subsidiaries are validly existing
and in good standing under the laws of their respective jurisdictions of organization, are duly qualified to do business and are in good standing in each jurisdiction in which their respective ownership or lease of property or the conduct of their
respective businesses requires such qualification, and have all power and authority necessary to own or hold their respective properties and to conduct the businesses in which they are engaged, except where the failure to be so qualified, in good
standing or have such power or authority would not reasonably be expect to, individually or in the aggregate, have 

  

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a material adverse effect on the business, assets, financial position or results of operations of the Company and its subsidiaries taken as a whole or on the
performance by the Company and the Guarantors of their obligations under the Securities and the Guarantees (a “Material Adverse Effect”). The Company does not own or control, directly or indirectly, any corporation, association or
other entity other than the subsidiaries listed in Schedule 2. 
 (b) Due Authorization. The Company and each of the Guarantors have
full right, power and authority to execute and deliver this Agreement, the Securities, the Indenture (including each Guarantee set forth therein), the Registration Rights Agreement and the Security Agreement (collectively, the “Transaction
Documents”) and to perform their respective obligations hereunder and thereunder; and all action required to be taken for the due and proper authorization, execution and delivery of each of the Transaction Documents and the consummation of
the transactions contemplated thereby has been duly and validly taken. 
 (c) The Indenture. The Indenture has been duly authorized by
the Company and each of the Guarantors and, when duly executed and delivered in accordance with its terms by each of the parties thereto and assuming the due authorization execution and delivery by each other party thereto, will constitute a valid
and legally binding agreement of the Company and each of the Guarantors enforceable against the Company and each of the Guarantors in accordance with its terms, except as enforceability may be limited by the Enforceability Exceptions; and on the
Closing Date, the Indenture will conform in all material respects to the requirements of the Trust Indenture Act of 1939, as amended (the “Trust Indenture Act”), and the rules and regulations of the Commission applicable to an
indenture that is qualified thereunder. 
 (d) The Securities and the Guarantees. The Securities have been duly authorized by the
Company and, when duly executed by the Company, authenticated by the Trustee in accordance with the provisions of the Indenture, issued and delivered as provided in the Indenture and paid for by the Purchasers as provided herein, will be duly and
validly issued and outstanding and will constitute valid and legally binding obligations of the Company enforceable against the Company in accordance with their terms, subject to the Enforceability Exceptions, and will be entitled to the benefits of
the Indenture; and the Guarantees have been duly authorized by each of the Guarantors and, when the Securities have been duly executed by the Company, authenticated by the Trustee in accordance with the provisions of the Indenture, issued and
delivered as provided in the Indenture and paid for by the Purchasers as provided herein, will be valid and legally binding obligations of each of the Guarantors, enforceable against each of the Guarantors in accordance with their terms, subject to
the Enforceability Exceptions, and will be entitled to the benefits of the Indenture. 
 (e) Purchase, Registration Rights and Security
Agreements. Each of this Agreement, the Registration Rights Agreement and the Security Agreement has been duly authorized by the Company and each of the Guarantors and when executed and delivered by the Company and each of the Guarantors, as
applicable, and each of the other parties thereto in accordance with its terms and assuming the due authorization, execution and delivery by each other party thereto, will constitute a valid and legally binding agreement of the Company and each of
the Guarantors, as applicable, enforceable against the Company and each of the Guarantors, as applicable, in accordance with its terms, subject to the Enforceability Exceptions, and except that rights to indemnity and contribution under this
Agreement and the Registration Rights Agreement may be limited by applicable law and public policy. 
  

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 (f) Collateral Documents, Financing Statements and Collateral. 
  

	 	(i)	The Security Agreement will be effective to grant a legal, valid and enforceable security interest in all of the grantor’s right, title and interest in the Collateral. Upon
filing of financing statements with respect to the Collateral described in the Security Agreement, the security interests granted thereby will constitute valid, perfected first priority liens and security interests in the Collateral for the benefit
of the Collateral Agent and the holders of the Securities, enforceable in accordance with the terms contained therein against all creditors of any grantor or mortgagor except in the case of liens perfected other than by the filing of financing
statements and subject only to Permitted Exceptions (as defined below) on the Collateral under the Indenture and except as such enforceability may be limited by the Enforceability Exceptions. 

  

	 	(ii)	The Company and the NetScout Guarantors, and to the knowledge of the Company and the NetScout Guarantors based solely on the information made available to the Company and the
NetScout Guarantors by the NetGen Guarantors, the NetGen Guarantors, collectively own, have rights in or have the power and authority to transfer rights in the Collateral, free and clear of any Liens (as defined in the Indenture), except such Liens
permitted to exist pursuant to Section 4.18 of the Indenture (the “Permitted Exceptions”). 

 (g)
Title to Property. The Company and the NetScout Guarantors, and to the knowledge of the Company and the NetScout Guarantors based solely on the information made available to the Company and the NetScout Guarantors by the NetGen Guarantors,
the NetGen Guarantors, have good and marketable title in fee simple to, or have valid rights to lease or otherwise use, all items of property that are described or referred to in the Security Agreement and any other property material to the
respective businesses of the Company and the Guarantors, in each case free and clear of all Liens other than the Permitted Exceptions. 
 (h)
Title to Intellectual Property. The Company and the NetScout Guarantors, and to the knowledge of the Company and the NetScout Guarantors based solely on the information made available to the Company and the NetScout Guarantors by the NetGen
Guarantors, the NetGen Guarantors, own or possess adequate rights to use all material patents, patent applications, trademarks, service marks, trade names, trademark registrations, service mark registrations, copyrights, licenses and know-how
(including trade secrets and other unpatented and/or unpatentable proprietary or confidential information, systems or procedures) necessary for the conduct of their respective businesses, except where such failure would not, individually or in the
aggregate, have a Material Adverse Effect; and the conduct of their respective businesses will not conflict in any material respect with any such rights of others, and the Company and the NetScout Guarantors, and to the knowledge of the Company and
the NetScout Guarantors based solely on the information made available to the Company and the NetScout Guarantors by the NetGen Guarantors, the NetGen Guarantors, have not received any notice of any claim of infringement of or conflict with any such
rights of others, which, if determined adversely to the Company or any Guarantor, would have a Material Adverse Effect. 
  

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 (i) Absence of Indebtedness. None of the Company or any of its subsidiaries other than Network
General Central Corporation and its subsidiaries, and to the knowledge of the Company and the NetScout Guarantors based solely on the information made available to the Company and the NetScout Guarantors by Network General Central Corporation and
its subsidiaries, none of Network General Central Corporation or any of its subsidiaries, has incurred any indebtedness for borrowed money other than indebtedness permitted to be outstanding under Section 4.17 of the Indenture. 
 (j) No Violation or Default. Neither the Company nor any of its subsidiaries other than Network General Central Corporation and its subsidiaries,
and to the knowledge of the Company and the NetScout Guarantors based solely on the information made available to the Company and the NetScout Guarantors by Network General Central Corporation and its subsidiaries, none of Network General Central
Corporation or any of its subsidiaries, is (i) in violation of its charter or by-laws or similar organizational documents; (ii) in default, and no event has occurred that, with notice or lapse of time or both, would constitute such a
default, in the due performance or observance of any term, covenant or condition contained in any indenture, mortgage, deed of trust, loan agreement or other agreement or instrument to which the Company or any of its subsidiaries is a party or by
which the Company or any of its subsidiaries is bound or to which any of the property or assets of the Company or any of its subsidiaries is subject; or (iii) in violation of any law or statute or any judgment, order, rule or regulation of any
court or arbitrator or governmental or regulatory authority, except, in the case of clauses (ii) and (iii) above, for any such default or violation that would not, individually or in the aggregate, have a Material Adverse Effect.

 (k) No Conflicts. The execution, delivery and performance by the Company and each of the Guarantors of each of the Transaction
Documents to which each is a party, the issuance and sale of the Securities (including the Guarantees) and compliance by the Company and each of the Guarantors with the terms thereof and the consummation of the transactions contemplated by the
Transaction Documents will not (i) conflict with or result in a breach or violation of any of the terms or provisions of, or constitute a default under, or result in the creation or imposition of any Lien (other than Liens created by the
Security Agreement) upon any property, assets or revenues of the Company or any of its subsidiaries other than Network General Central Corporation and its subsidiaries, and to the knowledge of the Company and the NetScout Guarantors based solely on
the information made available to the Company and the NetScout Guarantors by Network General Central Corporation and its subsidiaries, any of Network General Central Corporation or any of its subsidiaries, pursuant to, any indenture, mortgage, deed
of trust, loan agreement or other agreement or instrument to which the Company or any of its subsidiaries is a party or by which the Company or any of its subsidiaries is bound or to which any of the property or assets of the Company or any of its
subsidiaries is subject, (ii) result in any violation of the provisions of the charter or by-laws or similar organizational documents of the Company or any of its subsidiaries, or (iii) result in the violation of any law or statute or any
judgment, order, rule or regulation of any court or arbitrator or governmental or regulatory authority, except, in the case of clauses (i) and (iii) above, for any such conflict, breach, violation or default that would not, individually or
in the aggregate, have a Material Adverse Effect. 
  

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 (l) No Consents Required. No consent, approval, authorization, order, registration or
qualification of or with any court or arbitrator or governmental or regulatory authority is required for the execution, delivery and performance by the Company and each of the Guarantors of each of the Transaction Documents to which each is a party,
the issuance and sale of the Securities (including the Guarantees) and compliance by the Company and each of the Guarantors with the terms thereof and the consummation of the transactions contemplated by the Transaction Documents, except for such
consents, approvals, authorizations, orders and registrations or qualifications as may be required (i) under applicable state securities laws in connection with the purchase and resale of the Securities by the Purchasers and (ii) under the
Securities Act, the Trust Indenture Act and applicable state securities laws as contemplated by the Registration Rights Agreement. 
 (m)
Investment Company Act. Neither the Company nor any of the Guarantors is, and after giving effect to the offering and sale of the Securities and the application of the proceeds thereof as described in Section 4(a), none of the Company
nor any of the Guarantors will be, an “investment company” or an entity “controlled” by an “investment company” within the meaning of the Investment Company Act of 1940, as amended, and the rules and regulations of the
Commission thereunder (collectively, the “Investment Company Act”). 
 (n) Solvency. On and immediately after the
Closing Date, the Company (after giving effect to the issuance of the Securities and the transactions contemplated by the Merger Agreement) will be Solvent. As used in this paragraph, the term “Solvent” means, with respect to a
particular date, that on such date (i) the present fair market value (or present fair saleable value) of the assets of the Company is not less than the total amount required to pay the liabilities of the Company on its total existing debts and
liabilities (including contingent liabilities) as they become absolute and matured; (ii) the Company is able to realize upon its assets and pay its debts and other liabilities, contingent obligations and commitments as they mature and become
due in the normal course of business; (iii) assuming consummation of the issuance of the Securities as contemplated by this Agreement, the Company is not incurring debts or liabilities beyond its ability to pay as such debts and liabilities
mature; (iv) the Company is not engaged in any business or transaction, and does not propose to engage in any business or transaction, for which its property would constitute unreasonably small capital after giving due consideration to the
prevailing practice in the industry in which the Company is engaged; and (v) the Company is not a defendant in any civil action that would result in a judgment that the Company is or would become unable to satisfy. 
 (o) No Restrictions on Subsidiaries. No subsidiary of the Company other than Network General Central Corporation and its subsidiaries, and to the
knowledge of the Company and the NetScout Guarantors based solely on the information made available to the Company and the NetScout Guarantors by Network General Central Corporation and its subsidiaries, none of Network General Central Corporation
or any of its subsidiaries is currently prohibited, directly or indirectly, under any agreement or other instrument to which it is a party or is subject, from paying any dividends to the Company, from making any other distribution on such
subsidiary’s capital stock, from repaying to the Company any loans or advances to such subsidiary from the Company or from transferring any of such subsidiary’s properties or assets to the Company or any other subsidiary of the Company.

  

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 (p) No Broker’s Fees. Neither the Company nor any of its subsidiaries other than Network
General Central Corporation and its subsidiaries, and to the knowledge of the Company and the NetScout Guarantors based solely on the information made available to the Company and the NetScout Guarantors by Network General Central Corporation and
its subsidiaries, none of Network General Central Corporation or any of its subsidiaries is a party to any contract, agreement or understanding with any person (other than this Agreement) that would give rise to a valid claim against any of them or
any Purchaser for a brokerage commission, finder’s fee or like payment in connection with the offering and sale of the Securities. 
 (q) No Integration. Neither the Company nor any of its affiliates (as defined in Rule 501(b) of Regulation D) has, directly or through any agent, sold, offered for sale, solicited offers to buy or otherwise negotiated in respect of,
any security (as defined in the Securities Act), that is or will be integrated with the sale of the Securities in a manner that would require registration of the Securities under the Securities Act. 
 (r) No General Solicitation or Directed Selling Efforts. None of the Company or any of its affiliates or any other person acting on its or their
behalf (other than the Purchasers, as to which no representation is made) has (i) solicited offers for, or offered or sold, the Securities by means of any form of general solicitation or general advertising within the meaning of Rule 502(c) of
Regulation D or in any manner involving a public offering within the meaning of Section 4(2) of the Securities Act or (ii) engaged in any directed selling efforts within the meaning of Regulation S under the Securities Act. 
 (s) Securities Law Exemptions. Assuming the accuracy of the representations and warranties of the Purchasers contained in Section 1(b) and
their compliance with their agreements set forth therein, it is not necessary, in connection with the issuance and sale of the Securities to the Purchasers to register the Securities under the Securities Act or, except in connection with the
registration contemplated by the Registration Rights Agreement, to qualify the Indenture under the Trust Indenture Act. 
 4. Further
Agreements of the Company and the Guarantors. The Company and each of the Guarantors jointly and severally covenant and agree with each Purchaser that: 
 (a) Use of Proceeds. The Company will apply the net proceeds from the sale of the Securities to refinance the outstanding Loans (as defined in the NetGen Credit Agreement) under the NetGen Credit Agreement and
to complete the Merger (as defined in the Merger Agreement). 
 (b) No Resales by the Company. The Company will not, and will not
permit any of its affiliates (as defined in Rule 144 under the Securities Act) to, resell any of the Securities that have been acquired by any of them, except for Securities purchased by the Company or any of its affiliates and resold in a
transaction registered under the Securities Act. 
 (c) No Integration. Neither the Company nor any of its affiliates (as defined in
Rule 501(b) of Regulation D) will, directly or through any agent, sell, offer for sale, solicit offers to buy or otherwise negotiate in respect of, any security (as defined in the Securities Act), that is or will be integrated with the sale of the
Securities in a manner that would require registration of the Securities under the Securities Act. 
  

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 (d) No General Solicitation or Directed Selling Efforts. None of the Company or any of its
affiliates or any other person acting on its or their behalf (other than the Purchasers, as to which no covenant is given) will (i) solicit offers for, or offer or sell, the Securities by means of any form of general solicitation or general
advertising within the meaning of Rule 502(c) of Regulation D or in any manner involving a public offering within the meaning of Section 4(2) of the Securities Act or (ii) engage in any directed selling efforts within the meaning of
Regulation S, and all such persons will comply with the offering restrictions requirement of Regulation S. 
 (e) Perfection of Security
Interests. The Company and the Guarantors (i) shall use their commercially reasonable efforts to complete on or prior to the Closing Date all filings and other similar actions required in connection with the perfection of security interests
as and to the extent contemplated by the Security Agreement, except as set forth in the immediately following sentence, and (ii) shall take all actions necessary to maintain and to perfect security interests in any Collateral acquired after the
Closing Date, in each case as and to the extent contemplated by the Security Agreement. The Company and the Guarantors shall deliver to the Collateral Trustee, no later than 30 days (except as provided below) from the Closing Date:
(i) information sufficient in the reasonable opinion of the Collateral Trustee to permit filings with respect to the Liens on the Intellectual Property of the Company and the other Guarantors to be made with the United States Patent &
Trademark Office or the United States Copyright Office, as the case may be, (ii) sixty (60) days from the Closing Date, control agreements with respect to the deposit accounts and securities accounts listed on Schedule 3 to the Security
Agreement, reasonably satisfactory to the Collateral Trustee, executed by the Company and the Guarantors and the entities holding such accounts, (iii) sixty (60) days from the Closing Date, stock certificates and stock powers with respect
to the foreign subsidiaries listed on Schedule 2 to the Security Agreement, and (iv) any other items described in Schedule 3 to the Security Agreement. 
 5. Certain Agreements of the Purchasers. Each Purchaser, severally and not jointly, represents, warrants and agrees that: 
 (a) No Written Communications. Such Purchaser has not and will not use, authorize use of, refer to, or participate in the planning for use of, any written communication that constitutes an offer to sell or the
solicitation of an offer to buy the Securities. 
 (b) Cancellation of NetGen Indebtedness and Release of Related Liens. Such
Purchaser will deliver to the Company prior to the Closing Date an agreement executed by such Purchaser providing for the cancellation in its entirety, effective as of the Closing, of the NetGen Indebtedness of NetGen Opco to such Purchaser. Such
Purchaser will provide its commercially reasonable assistance to the Company in connection with the release of any Liens on the assets, properties and revenues of NetGen Opco and its subsidiaries securing the NetGen Indebtedness and the other
obligations of NetGen Opco pursuant to the NetGen Credit Agreement. 
 6. Conditions of Purchasers’ Obligations. The obligation
of each Purchaser to purchase Securities on the Closing Date as provided herein is subject to the performance by the Company and each of the Guarantors of their respective covenants and other obligations hereunder and to the following additional
conditions: 
 (a) Representations and Warranties. The representations and warranties of the Company and the Guarantors contained
herein shall be true and correct on the date hereof and on and as of the Closing Date (except for representations and warranties that speak as 

  

 11 








 
of a specific date which shall be true and correct as of such date); and the statements of the Company, the Guarantors and their respective officers made in
any certificates delivered pursuant to this Agreement shall be true and correct on and as of the Closing Date. 
 (b) Officer’s
Certificate. The Purchasers shall have received on and as of the Closing Date a certificate of an executive officer of the Company and of each Guarantor who has specific knowledge of the Company’s or such Guarantor’s financial matters
and is reasonably satisfactory to the Purchasers confirming that, to such officer’s knowledge, the representations and warranties of the Company and the Guarantors in this Agreement are true and correct and that the Company and the Guarantors
have complied with all agreements and satisfied all conditions on their part to be performed or satisfied hereunder at or prior to the Closing Date. 
 (c) Opinion of Counsel for the Company. Cooley Godward Kronish LLP, counsel for the Company, shall have furnished to the Purchasers, at the request of the Company, their written opinion, dated the Closing Date
and addressed to the Purchasers, in form and substance reasonably satisfactory to the Purchasers, to the effect set forth in Annex A hereto. 
 (d) No Legal Impediment to Issuance. No action shall have been taken and no statute, rule, regulation or order shall have been enacted, adopted or issued by any federal, state or foreign governmental or regulatory authority that
would, as of the Closing Date, prevent the issuance or sale of the Securities or the issuance of the Guarantees; and no injunction or order of any federal, state or foreign court shall have been issued that would, as of the Closing Date, prevent the
issuance or sale of the Securities or the issuance of the Guarantees. 
 (e) Good Standing. The Purchasers shall have received on and
as of the Closing Date satisfactory evidence of the good standing of the Company and each Guarantor in their respective jurisdictions of organization and their good standing in such other jurisdictions as the Purchasers may reasonably request, in
each case in writing or any standard form of telecommunication, from the appropriate governmental authorities of such jurisdictions. 
 (f)
Indenture. The Indenture shall have executed and delivered by a duly authorized officer of the Company, each of the Guarantors and the Trustee. 
 (g) Registration Rights Agreement. The Purchasers shall have received a counterpart of the Registration Rights Agreement that shall have been executed and delivered by a duly authorized officer of the Company
and each of the Guarantors. 
 (h) Lien Searches and Title Searches. The Purchasers shall have received the results of a recent
Uniform Commercial Code lien search and/or title search in the State of Massachusetts and in each of the jurisdictions in which the Company and the Guarantors are organized, and such search shall reveal no liens on any of the assets of the
Guarantors or the Company except for the Permitted Exceptions and Liens to be released on the Closing Date. 
 (i) Security Agreement.
The Purchasers shall have received conformed counterparts of the Security Agreement that shall have been executed and delivered by duly authorized officers of each party thereto, in form and substance reasonably satisfactory to the Purchasers.

  

 12 








 (j) Filings, Registration and Recordings. Except as otherwise contemplated by the Security
Agreement, each document (including any Uniform Commercial Code financing statement) required by the Security Agreement, or under law or reasonably requested by the Purchasers, in each case, to be filed, registered or recorded, or delivered for
filing on or prior to the Closing Date, in order to create in favor of the Collateral Agent, for the benefit of the holders of the Securities, a perfected first priority lien and security interest in the Collateral, which can be perfected by the
making of such filings, registrations or recordations prior and superior to the right of any other person (other than the Permitted Exceptions), shall be in proper form for filing, registration or recordation. 
 (k) Additional Documents. On or prior to the Closing Date, the Company and the Guarantors shall have furnished to the Purchasers such further
certificates and documents as the Purchasers may reasonably request. 
 All opinions, letters, certificates and evidence mentioned above or
elsewhere in this Agreement shall be deemed to be in compliance with the provisions hereof only if they are in form and substance reasonably satisfactory to counsel for the Purchasers. 
 7. Conditions of Company’s and Guarantors’ Obligations. The obligations of the Company and each of the Guarantors to perform under the
Transaction Documents on the Closing Date is subject to the performance by the Purchasers of their respective covenants and other obligations hereunder and to the following additional conditions: 
 (a) Representations and Warranties. The representations and warranties in Section 1(b) made by the Purchasers shall be true and correct in all
material respects at the Closing Date, with the same force and effect as if they had been made on and as of said date. 
 (b) Agreements.
The Purchasers shall have performed and complied with all agreements and conditions herein required to be performed or complied with by such Purchasers on or before the Closing Date. 
 (c) Execution. The Purchasers shall have executed each of the Transaction Documents to which it is a party and delivered the same to the Company.

 (d) Purchase Price. The Purchasers shall have paid the purchase price for the Securities in accordance with Section 2(b)
hereof. 
 (e) Existing Credit Agreement. The Purchasers shall hold an aggregate of $98,500,000 of outstanding principal amount of
indebtedness of Network General Corporation pursuant to the Credit Agreement, dated as of July 16, 2004 and as subsequently amended, between Network General Corporation and the Purchasers. 
 8. Payment of Expenses. Whether or not the transactions contemplated by this Agreement are consummated or this Agreement is terminated, the
Company and each of the Guarantors jointly and severally agree to pay or cause to be paid all costs and expenses incident to the performance of their respective obligations hereunder, including without limitation, (i) the costs incident to the
authorization, issuance, sale, preparation and delivery of the Securities and any taxes payable in that connection; (ii) the costs of reproducing and distributing each of the Transaction Documents and perfecting the security interest in the
Collateral as contemplated by the Security Agreement; (iii) the fees and expenses of the Company’s and the Guarantors’ counsel and independent accountants; 

  

 13 








 
(iv) all reasonable fees, disbursements and other charges of legal counsel for the Purchasers not to exceed $35,000 related to securing the assets
pursuant to the terms of the offering of the Securities contemplated hereby (including the preparation of all instruments and documentation and the making of all filings related thereto); and (v) the fees and expenses of the Trustee, any paying
agent and any collateral agent (including related fees and expenses of any counsel to such parties). 
 9. Persons Entitled to Benefit of
Agreement. This Agreement shall inure to the benefit of and be binding upon the parties hereto and their respective successors and any controlling persons referred to herein. Nothing in this Agreement is intended or shall be construed to give
any other person any legal or equitable right, remedy or claim under or in respect of this Agreement or any provision contained herein. No purchaser of Securities from any Purchaser shall be deemed to be a successor merely by reason of such
purchase. 
 10. Survival. The respective representations, warranties and agreements of the Company, the Guarantors and the Purchasers
contained in this Agreement or made by or on behalf of the Company, the Guarantors or the Purchasers pursuant to this Agreement or any certificate delivered pursuant hereto shall survive the delivery of and payment for the Securities and shall
remain in full force and effect, regardless of any termination of this Agreement or any investigation made by or on behalf of the Company, the Guarantors or the Purchasers. 
 11. Certain Defined Terms. For purposes of this Agreement, (a) except where otherwise expressly provided, the term
“affiliate” has the meaning set forth in Rule 405 under the Securities Act; (b) the term “subsidiary” has the meaning set forth in Rule 405 under the Securities Act; and (c) the term
“Lien” has the meaning set forth in the Indenture. 
 12. Miscellaneous. (a) Notices. All notices and
other communications hereunder shall be in writing and shall be deemed to have been duly given if mailed or transmitted and confirmed by any standard form of telecommunication. Notices to the Purchasers shall be given to the following as applicable:

 Integral Capital Partners VI, L.P. 
 3000 Sand Hill Road 
 Building 3, Suite 240 
 Menlo Park, CA 94025 
 Attention: Pamela K. Hagenah 
 Fax: (650) 233-0366 
 Silver Lake
Partners, L.P. 
 Silver Lake Investors, L.P. 
 Silver Lake Technology Investors, L.L.C. 
 2775 Sand Hill Road, Suite 100 
 Menlo Park, California 94025 
 Attention:
General Counsel 
 Fax: (650) 234-2502 
  

 14 








 T3 Starburst II, LLC 
 TPG Starburst III, LLC 
 TPG Starburst IV, LLC 
 301 Commerce Street

 Suite 3300 
 Fort Worth, TX
76102 
 Attention: John Riola 
 Fax: (817) 850-4023 
 Notices to the Company and the Guarantors shall be given to them at the following: 
 NetScout Systems, Inc. 
 310 Littleton Road

 Westford, Massachusetts 01886 
 Attn.: President and Chief Executive Officer 
 Fax: (978) 614-4039 
 (b) Governing Law. This Agreement shall be governed by and construed in accordance with the laws of the State of New York. 
 (c) Counterparts. This Agreement may be signed in counterparts (which may include counterparts delivered by any standard form of
telecommunication), each of which shall be an original and all of which together shall constitute one and the same instrument. 
 (d)
Amendments or Waivers. No amendment or waiver of any provision of this Agreement, nor any consent or approval to any departure therefrom, shall in any event be effective unless the same shall be in writing and signed by the parties hereto.

 (e) Headings. The headings herein are included for convenience of reference only and are not intended to be part of, or to affect
the meaning or interpretation of, this Agreement. 
 [remainder of page intentionally left blank] 
  

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 If the foregoing is in accordance with your understanding, please indicate your acceptance of this Agreement by signing
in the space provided below. 
  

			
	Very truly yours,
	
	NETSCOUT SYSTEMS, INC.
		
	By:	 	 /s/ David P. Sommers

	Name:	 	David P. Sommers
	Title:	 	 Chief Financial Officer and Senior Vice
 President,
General Operations

	
	NETSCOUT SYSTEMS SECURITY CORPORATION
		
	By:	 	 /s/ David P. Sommers

	Name:	 	David P. Sommers
	Title:	 	President
	
	NETSCOUT SERVICE LEVEL CORPORATION
		
	By:	 	 /s/ David P. Sommers

	Name:	 	David P. Sommers
	Title:	 	President


  

 16 









			
	NETWORK GENERAL CENTRAL
CORPORATION
		
	By:	 	 /s/ David P. Sommers

	Name:	 	David P. Sommers
	Title:	 	Treasurer
	
	NETWORK GENERAL CORPORATION
		
	By:	 	 /s/ David P. Sommers

	Name:	 	David P. Sommers
	Title:	 	Treasurer
	
	FIDELIA TECHNOLOGY, INC.
		
	By:	 	 /s/ David P. Sommers

	Name:	 	David P. Sommers
	Title:	 	President
	
	 NETWORK GENERAL INTERNATIONAL
 CORPORATION


		
	By:	 	 /s/ David P. Sommers

	Name:	 	David P. Sommers
	Title:	 	President
	
	STARBURST TECHNOLOGY HOLDINGS I, LLC
		
	By:	 	 /s/ David P. Sommers

	Name:	 	David P. Sommers
	Title:	 	President
	
	STARBURST TECHNOLOGY HOLDINGS II, LLC
		
	By:	 	 /s/ David P. Sommers

	Name:	 	David P. Sommers
	Title:	 	President









 Accepted: November 1, 2007 
  

			
	INTEGRAL CAPITAL PARTNERS VI, L.P.
		
	By:	 	Integral Capital Management VI, L.L.C.,
		 	its General Partner
		
	By:	 	 /s/ Pamela K. Hagenah

	Name:	 	Pamela K. Hagenah
	Title:	 	Manager

  

 18 









			
	SILVER LAKE PARTNERS, L.P.
		
	By:	 	Silver Lake Technology Associates, L.L.C.
		 	its General Partner
		
	By:	 	Silver Lake Group, L.L.C.
		 	its Managing Member
		
	By:	 	 /s/ Jim Davidson

	Name:	 	Jim Davidson
	Title:	 	Managing Director
	
	SILVER LAKE INVESTORS, L.P.
		
	By:	 	Silver Lake Technology Associates, L.L.C.
		 	its General Partner
		
	By:	 	Silver Lake Group, L.L.C.
		 	its Managing Member
		
	By:	 	 /s/ Jim Davidson

	Name:	 	Jim Davidson
	Title:	 	Managing Director
	
	SILVER LAKE TECHNOLOGY INVESTORS, L.L.C.
		
	By:	 	Silver Lake Partners Management Company, L.L.C.,
		 	its Manager
		
	By:	 	 /s/ Jim Davidson

	Name:	 	Jim Davidson
	Title:	 	Managing Director









			
	TPG STARBURST IV, LLC
		
	By:	 	TPG Partners IV, L.P.,
		 	its Manager
		
	By:	 	TPG GenPar IV, L.P.,
		 	its General Partner
		
	By:	 	TPG Advisors IV, Inc.,
		 	its General Partner
		
	By:	 	 /s/ Bryan Taylor

	Name:	 	Bryan Taylor
	Title:	 	Partner
	
	TPG STARBURST III, LLC
		
	By:	 	TPG Partners III, L.P.,
		 	its Manager
		
	By:	 	TPG GenPar III, L.P.,
		 	its General Partner
		
	By:	 	TPG Advisors III, Inc.,
		 	its General Partner
		
	By:	 	 /s/ Bryan Taylor

	Name:	 	Bryan Taylor
	Title:	 	Partner









			
	T3 STARBURST II, LLC
		
	By:	 	T3 Partners II, L.P.,
		 	its Manager
		
	By:	 	T3 Gen Par II, L.P.,
		 	its General Partner
		
	By:	 	T3 Advisors II, Inc.
		 	its General Partner
		
	By:	 	 /s/ Bryan Taylor

	Name:	 	Bryan Taylor
	Title:	 	Partner

  

 21 








 Schedule 1 
  

				
	 Purchaser
	  	Principal Amount
	 Silver Lake Partners, L.P.
	  	$	46,035,000
	 Silver Lake Investors, L.P.
	  	$	1,295,000
	 Silver Lake Technology Investors, LLC
	  	$	169,000
	 TPG Starburst IV, LLC
	  	$	20,538,000
	 TPG Starburst III, LLC
	  	$	12,796,000
	 T3 Starburst II LLC
	  	$	16,667,000
	 Integral Capital Partners VI, L.P.
	  	$	2,500,000
		  	 	 
	 Total
	  	$	100,000,000
		  	 	 








 Schedule 2 
 List of Guarantors 
 NETSCOUT GUARANTORS 
 NetScout Systems Security Corporation 
 NetScout Service Level Corporation 
 NETGEN GUARANTORS 
 Network General Central Corporation 
 Network General Corporation 
 Fidelia Technology, Inc. 
 Network General International Corporation 
 Starburst Technology Holdings I,
LLC 
 Starburst Technology Holdings II, LLC 
 NON GUARANTOR
NETSCOUT SUBSIDIARIES 
 NetScout Systems Canada, Inc. 
 NetScout Systems France, SARL 
 NetScout Systems Germany GmbH 
 NetScout Systems (HK) Limited 
 NetScout Systems India Private Limited 
 NetScout Systems Japan K.K. 
 NetScout Systems Mexico, S.A. de C.V. 
 NetScout Systems Norway AS 
 NetScout Systems Singapore Pte Ltd 
 NetScout Systems Switzerland GmbH 
 NetScout Systems (UK) Limited 

 

 23 








 Servicios A Terceros, S.C. Civil Society 
 NetScout Systems Australia Pty Ltd 
 NON GUARANTOR NETGEN SUBSIDIARIES 
 Network General Brazil Comercio e Servicos Ltda 
 Network General de Costa
Rica, S.A. 
 Network General Japan KK 
 Network General Holdings
Cayman 
 Network General Software India Private Limited 
 Network
General Europe, Ltd. 
 Network General Technology 
 Network
General Asia Pte. Ltd. 
 Network General, BV 
 Network General
Deutschland GmbH 
  

 24 








 THE FOLLOWING SCHEDULES TO THE PURCHASE AGREEMENT HAVE BEEN OMITTED IN ACCORDANCE WITH ITEM 601(B)(2) OF REGULATION
S-K. 
 Disclosure Schedules 
 Section 3(g) –
Title to Property 
 Section 3(h) – Title to Intellectual Property 
 Section 3(j) – No Violation or Default 
 Section 3(k) – Conflicts 
 Section 3(l) – Consents 
 NetScout Systems, Inc. will furnish
supplementally a copy of any omitted schedule to the Securities and Exchange Commission upon request, provided however that NetScout Systems, Inc. may request confidential treatment pursuant to Rule 24b-2 of the Securities and Exchange Act of 1934,
as amended for any schedule so furnished. 
  

 25