**Exhibit 10.38.3****AMENDMENT NO. 6 TO CREDIT AGREEMENT**     This Amendment No. 6 to Credit Agreement (this “Agreement”) dated as of August 10,2006 is made by and between **NEUSTAR, INC.**, a Delaware corporation having its principal place ofbusiness in Sterling, Virginia (the “Borrower”), and **BANK OF AMERICA, N.A.**, a nationalbanking association organized and existing under the laws of the United States (“Bank ofAmerica”), in its capacity as administrative agent for the Lenders (as defined in the CreditAgreement (as defined below)) (in such capacity, the “Administrative Agent”), and each ofthe Lenders signatory hereto, and each of the Guarantors (as defined in the Credit Agreement)signatory hereto.**W I T N E S S E T H****:**     **WHEREAS**, the Borrower, the Administrative Agent and the Lenders have entered into that certainCredit Agreement dated as of August 14, 2002, as amended by Amendment No. 1 to Credit Agreementdated as of October 1, 2003, Amendment No. 2 to Credit Agreement dated as of August 30, 2004,Amendment No. 3 to Credit Agreement and Waiver dated as of February 15, 2005, Amendment No. 4 toCredit Agreement dated as of August 12, 2005, and Amendment No. 5 to Credit Agreement dated as ofFebruary 10, 2006 (and as hereby amended and as from time to time hereafter further amended,modified, supplemented, restated, or amended and restated, the “Credit Agreement”;capitalized terms used in this Agreement not otherwise defined herein shall have the respectivemeanings given thereto in the Credit Agreement), pursuant to which the Lenders have made availableto the Borrower a revolving credit facility, including a letter of credit facility; and     **WHEREAS**, the Maturity Date of such revolving credit facility is August 10, 2006; and     **WHEREAS,**the Borrower has requested that the Credit Agreement be amended to extend theMaturity Date to November 8, 2006;     **NOW, THEREFORE,**in consideration of the premises and further valuable consideration, thereceipt and sufficiency of which is hereby acknowledged, the parties hereto agree as follows:     1. Amendment to Credit Agreement. Subject to the terms and conditions set forthherein, Section 1.01 of the Credit Agreement is amended to restate the definitions of “MaturityDate” in its entirety to read as follows:          “Maturity Date” means November 8, 2006.     2. Effectiveness; Conditions Precedent. The effectiveness of this Agreement and theamendments to the Credit Agreement herein provided are subject to the satisfaction of the followingconditions precedent:
 

 
     (a) the Administrative Agent shall have received each of the following documents orinstruments in form and substance reasonably acceptable to the Administrative Agent: (i) four (4) original counterparts of thisAgreement, duly executed by the Borrower, the Administrative Agent,each Guarantor and the Required Lenders; and  (ii) such other documents, instruments, opinions,certifications, undertakings, further assurances and other matters asthe Administrative Agent shall reasonably request; and     (b) all fees and expenses payable to the Administrative Agent and the Lenders(including the reasonable fees and expenses of counsel to the Administrative Agent estimatedto date) shall have been paid in full (without prejudice to final settling of accounts forsuch fees and expenses).     3. Consent of the Guarantors. Each Guarantor hereby consents, acknowledges and agreesto the amendments set forth herein and hereby confirms and ratifies in all respects the Guaranty towhich such Guarantor is a party (including without limitation the continuation of such Guarantor’spayment and performance when due of the obligations thereunder upon and after the effectiveness ofthis Agreement and the amendments contemplated hereby) and the enforceability of such Guarantyagainst such Guarantor in accordance with its terms.     4. Representations and Warranties. In order to induce the Administrative Agent andthe Lenders to enter into this Agreement, the Borrower represents and warrants to theAdministrative Agent and the Lenders as follows:     (a) The representations and warranties made by the Borrower in Article VI ofthe Credit Agreement and in each of the other Loan Documents to which it is a party are trueand correct on and as of the date hereof, except to the extent that such representations andwarranties expressly relate to an earlier date;     (b) Since the date of the most recent financial reports of the Borrower deliveredpursuant to Section 7.01 of the Credit Agreement, no act, event, condition orcircumstance has occurred or arisen which, singly or in the aggregate with one or more otheracts, events, occurrences or conditions (whenever occurring or arising), has had or couldreasonably be expected to have a Material Adverse Effect;     (c) The Persons appearing as Guarantors on the signature pages to this Agreementconstitute all Persons who are required to be Guarantors pursuant to the terms of the CreditAgreement and the other Loan Documents, (except as may have been waived in writing by theRequired Lenders) including without limitation all Persons who became Subsidiaries or wereotherwise required to become Guarantors after the Closing Date, and each of such Persons hasbecome and remains a party to a Guaranty as a Guarantor;
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     (d) This Agreement has been duly authorized, executed and delivered by the Borrower andthe Guarantors and constitutes a legal, valid and binding obligation of such parties, exceptas may be limited by general principles of equity or by the effect of any applicablebankruptcy, insolvency, reorganization, moratorium or similar law affecting creditors’rights generally; and     (e) No Default or Event of Default has occurred and is continuing.     5. Entire Agreement. This Agreement, together with all the Loan Documents(collectively, the “Relevant Documents”), sets forth the entire understanding and agreementof the parties hereto in relation to the subject matter hereof and supersedes any priornegotiations and agreements among the parties relating to such subject matter. No promise,condition, representation or warranty, express or implied, not set forth in the Relevant Documentsshall bind any party hereto, and no such party has relied on any such promise, condition,representation or warranty. Each of the parties hereto acknowledges that, except as otherwiseexpressly stated in the Relevant Documents, no representations, warranties or commitments, expressor implied, have been made by any party to the other. None of the terms or conditions of thisAgreement may be changed, modified, waived or canceled orally or otherwise, except in writing andin accordance with Section 11.01 of the Credit Agreement.     6. Full Force and Effect of Agreement. Except as hereby specifically amended,modified or supplemented, the Credit Agreement and all other Loan Documents are hereby confirmedand ratified in all respects and shall be and remain in full force and effect according to theirrespective terms.     7. Counterparts. This Agreement may be executed in any number of counterparts, eachof which shall be deemed an original as against any party whose signature appears thereon, and allof which shall together constitute one and the same instrument.     8. Governing Law. This Agreement shall in all respects be governed by, and construedin accordance with, the laws of the State of New York applicable to contracts executed and to beperformed entirely within such State, and shall be further subject to the provisions of Section11.16 of the Credit Agreement.     9. Enforceability. Should any one or more of the provisions of this Agreement bedetermined to be illegal or unenforceable as to one or more of the parties hereto, all otherprovisions nevertheless shall remain effective and binding on the parties hereto.     10. References. All references in any of the Loan Documents to the “Credit Agreement”shall mean the Credit Agreement, as amended hereby.     11. Successors and Assigns. This Agreement shall be binding upon and inure to thebenefit of the Borrower, the Administrative Agent and each of the Guarantors and the Lenders, andtheir respective successors, legal representatives, and assignees to the extent such assignees arepermitted assignees as provided in Section 11.07 of the Credit Agreement.
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     I**N WITNESS WHEREOF**, the parties hereto have caused this Amendment No. 6 to Credit Agreement tobe made, executed and delivered by their duly authorized officers as of the day and year firstabove written.                **BORROWER****:**           **NEUSTAR, INC.**           By: /s/ Jeffrey E. Ganek           Name: Jeffrey E. Ganek    Title: Chairman and CEO           **GUARANTORS:**           **BIZTELONE, INC.**           By: /s/ Jeffrey E. Ganek           Name: Jeffrey E. Ganek    Title: President and CEO           **ULTRADNS CORPORATION**           By: /s/ Jeffrey E. Ganek           Name: Jeffrey E. Ganek    Title: Chairman  Signature Page 1 of 3
 

 
                **ADMINISTRATIVE AGENT****:**           **BANK OF AMERICA, N.A., as Administrative Agent**           By: /s/ Elizabeth F. Shore           Name: Elizabeth F. Shore    Title: Senior Vice President  Signature Page 2 of 3
 

 
                **LENDERS:**           **BANK OF AMERICA, N.A.**           By: /s/ Elizabeth F. Shore           Name: Elizabeth F. Shore    Title: Senior Vice President  Signature Page 3 of 3