EXHIBIT 10.43
 NONQUALIFIED STOCK OPTION AGREEMENT
UNDER THE
NEUSTAR, INC. 1999 EQUITY INCENTIVE PLAN
 December 18, 2003 Martin Lowen
 WITNESSETH
   Grant of Option 35,487 $9.00
 Limitations
on Exercise of Options
 Termination of Service
  1




---



##### 



Non-Transferable
 Adjustments and Corporate Reorganizations; Changes in Organization.
  2




---



##### 



3




---



##### 



4




---



##### 



Exercise: Payment For and Delivery of Common Stock provided however i.e.
 Rights as Common Stockholder
 Company; Participant
  5




---



##### 



Requirements of Law
   Notices
 Disposition of Common Stock
 Binding Effect
 Plan
 6




---



##### 



Governing Law
 Entire Agreement
   NEUSTAR, INC.By:
    /s/ Jeffrey GanekName:
    Jeffrey GanekTitle:
    Chairman and Chief Executive Officer ACCEPTED:/s/ Martin Lowen

Martin Lowen
 7




---



##### 



NONQUALIFIED STOCK OPTION AGREEMENT AMENDMENT
 Amendment
 WITNESSETH
    NOW, THEREFORE,
 Amendment to Section 5 (d) and 5(e) of the Option Agreement




---



##### 



(i)
    
    A substantial diminution or material adverse
change in the Participants status, title, position,
authority, duties or responsibilities (including reporting
responsibilities) as in effect immediately prior to a
Corporate Transaction, except in connection with the
Participants termination of Service with the Company for
Cause, disability, death or by the Participant other than for
Good Reason.(ii)
    
    A reduction in the Participants annual base salary,
except in connection with an across-the-board salary
reduction of less than ten percent (10%) affecting all
senior executives of the Company.(iii)
    
    The Successor Corporations
failure to cover the Participant under employee benefit plans,
programs and practices that, in the aggregate, provide
substantially comparable benefits (from an economic perspective) to
the Participant




---



##### 



relative to the benefits and total costs under the
material employee benefit plans, programs and practices in
which the Participant (and/or his family or dependents) is
participating immediately preceding the Corporate
Transaction.(iv)
    
    The Successor Corporations requiring the
Participant to be based at any office location that is
more than fifty (50) miles further from the Participants
office location immediately prior to a Corporate
Transaction; except for reasonable required travel for the
Successor Corporations business that is not materially
greater than such travel requirements prior to such
Corporate Transaction.(v)
    
    A material breach by the Successor Corporation
of its obligations to the Participant under the
Plan.
 Entire Agreement
 Full Force and Effect of Agreement
 Counterparts
 Governing Law




---



##### 



WITNESS WHEREOF,
 NEUSTAR, INC.By:
    /s/ Jeffrey E. GanekName:
    Jeffrey E. GanekTitle:
    Chairman and Chief Executive OfficerOPTIONEE:Martin Lowen/s/ Martin Lowen




---



##### 



NONQUALIFIED STOCK OPTION AGREEMENT AMENDMENT
 Amendment
 WITNESSETH
    NOW, THEREFORE,
 Amendment to Section 5 of the Option Agreement




---



##### 



(i)
    
    A substantial diminution or material adverse change in the Participants
status, title, position, authority, duties or responsibilities (including
reporting responsibilities) as in effect immediately prior to a Corporate
Transaction, except in connection with the Participants termination of
 2




---



##### 



Service with the Company for Cause, disability, death or by the
Participant other than for Good Reason.
 (ii)
    
    A reduction in the Participants annual base salary.(iii)
    
    The Successor Corporations failure to cover the Participant under
employee benefit plans, programs and practices that, in the aggregate,
provide substantially comparable benefits (from an economic perspective) to
the Participant relative to the benefits and total costs under the material
employee benefit plans, programs and practices in which the Participant
(and/or his family or dependents) is participating immediately preceding
the Corporate Transaction.(iv)
    
    The Successor Corporations requiring the Participant to be based at any
office location that is more than fifty (50) miles further from the
Participants office location immediately prior to a Corporate Transaction;
except for reasonable required travel for the Successor Corporations
business that is not materially greater than such travel requirements prior
to such Corporate Transaction.(v)
    
    A material breach by the Successor Corporation of its
obligations to the Participant under the Plan.
 Entire Agreement
 Full Force and Effect of Agreement
 Counterparts
 Governing Law
 3




---



##### 



IN WITNESS WHEREOF,
 NEUSTAR, INC.By:
    /s/ Jeffrey E. GanekName:
    Jeffrey E. GanekTitle:
    Chairman and Chief Executive OfficerOPTIONEE:Martin Lowen/s/ Martin Lowen 4