Ownership Submission
FORM 4
Check this box if no longer subject to Section 16. Form 4 or Form 5 obligations may continue. See Instruction 1(b).
UNITED STATES SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

STATEMENT OF CHANGES IN BENEFICIAL OWNERSHIP OF SECURITIES

Filed pursuant to Section 16(a) of the Securities Exchange Act of 1934, Section 17(a) of the Public Utility Holding Company Act of 1935 or Section 30(h) of the Investment Company Act of 1940
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(Print or Type Responses)
1. Name and Address of Reporting Person *
Reilly Thomas
  2. Issuer Name and Ticker or Trading Symbol
ArcSight Inc [ARST]
5. Relationship of Reporting Person(s) to Issuer
(Check all applicable)
__X__ Director _____ 10% Owner
__X__ Officer (give title below) _____ Other (specify below)
President and CEO
(Last)
(First)
(Middle)
C/O ARCSIGHT, INC., 5 RESULTS WAY
3. Date of Earliest Transaction (Month/Day/Year)
10/21/2010
(Street)

CUPERTINO, CA 95014
4. If Amendment, Date Original Filed(Month/Day/Year)
6. Individual or Joint/Group Filing(Check Applicable Line)
_X_ Form filed by One Reporting Person
___ Form filed by More than One Reporting Person
(City)
(State)
(Zip)
Table I - Non-Derivative Securities Acquired, Disposed of, or Beneficially Owned
1.Title of Security
(Instr. 3)
2. Transaction Date (Month/Day/Year) 2A. Deemed Execution Date, if any (Month/Day/Year) 3. Transaction Code
(Instr. 8)
4. Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4 and 5)
5. Amount of Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 3 and 4)
6. Ownership Form: Direct (D) or Indirect (I)
(Instr. 4)
7. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V Amount (A) or (D) Price
Common Stock 10/21/2010   U(1)   6,795 D $ 43.5 0 D  
Common Stock 10/21/2010   M   14,092 (2) A $ 6.8 14,092 D  
Common Stock 10/22/2010   D(3)   14,092 D $ 43.5 0 D  

Reminder: Report on a separate line for each class of securities beneficially owned directly or indirectly.
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Table II - Derivative Securities Acquired, Disposed of, or Beneficially Owned
(e.g., puts, calls, warrants, options, convertible securities)
1. Title of Derivative Security
(Instr. 3)
2. Conversion or Exercise Price of Derivative Security 3. Transaction Date (Month/Day/Year) 3A. Deemed Execution Date, if any (Month/Day/Year) 4. Transaction Code
(Instr. 8)
5. Number of Derivative Securities Acquired (A) or Disposed of (D)
(Instr. 3, 4, and 5)
6. Date Exercisable and Expiration Date
(Month/Day/Year)
7. Title and Amount of Underlying Securities
(Instr. 3 and 4)
8. Price of Derivative Security
(Instr. 5)
9. Number of Derivative Securities Beneficially Owned Following Reported Transaction(s)
(Instr. 4)
10. Ownership Form of Derivative Security: Direct (D) or Indirect (I)
(Instr. 4)
11. Nature of Indirect Beneficial Ownership
(Instr. 4)
Code V (A) (D) Date Exercisable Expiration Date Title Amount or Number of Shares
Stock Option (Right to Buy) $ 6.8 10/22/2010   D     14,705   (2)(4) 01/23/2017 Common Stock 14,705 (2) 0 D  
Stock Option (Right to Buy) $ 6.8 10/22/2010   D     775,575   (4) 01/23/2017 Common Stock 775,575 (5) 0 D  
Stock Option (Right to Buy) $ 6.8 10/22/2010   D     290,484   (4) 01/23/2017 Common Stock 290,484 (6) 0 D  
Stock Option (Right to Buy) $ 8.5 10/22/2010   D     46,313   (7) 06/17/2018 Common Stock 46,313 (8) 0 D  
Stock Option (Right to Buy) $ 7.76 10/22/2010   D     200,000   (9) 09/30/2018 Common Stock 200,000 (10) 0 D  
Stock Option (Right to Buy) $ 7.76 10/22/2010   D     200,000   (11) 09/30/2018 Common Stock 200,000 (12) 0 D  
Stock Option (Right to Buy) $ 18 10/22/2010   D     125,000   (13) 06/08/2019 Common Stock 125,000 (14) 0 D  
Stock Option (Right to Buy) $ 21.63 10/22/2010   D     131,500   (15) 05/18/2020 Common Stock 131,500 (16) 0 D  

Reporting Owners

Reporting Owner Name / Address Relationships
 Director  10% Owner  Officer  Other
Reilly Thomas
C/O ARCSIGHT, INC.
5 RESULTS WAY
CUPERTINO, CA 95014
  X     President and CEO  

Signatures

 /s/ Tram T. Phi as attorney-in-fact for Thomas Reilly   10/25/2010
**Signature of Reporting Person Date

Explanation of Responses:

* If the form is filed by more than one reporting person, see Instruction 4(b)(v).
** Intentional misstatements or omissions of facts constitute Federal Criminal Violations. See 18 U.S.C. 1001 and 15 U.S.C. 78ff(a).
(1) Pursuant to the terms of the tender offer by Priam Acquisition Corporation, a Delaware corporation ("Purchaser") and a wholly-owned, direct or indirect, subsidiary of Hewlett-Packard Company, a Delaware corporation ("HP"), to purchase all outstanding shares of Issuer Common Stock, disclosed in the Tender Offer Statement on Schedule TO filed with the Securities and Exchange Commission (the "Tender Offer"), Purchaser accepted for payment of $43.50 per share all shares validly tendered on or prior to October 20, 2010.
(2) 14,092 shares under this option were exercised pursuant to a conditional exercise program effective on the satisfaction of the closing conditions to the merger (the "Merger") contemplated by that certain Agreement and Plan of Merger by and among the Issuer, HP and Purchaser, dated as of September 13, 2010 (the "Merger Agreement"), and such shares were converted into the right to receive $43.50 per share and the remaining shares under the option were assumed and exchanged for an option to purchase 622 shares of HP Common Stock at an exercise price per share of $6.70.
(3) All shares issued and outstanding immediately prior to the effectiveness of the Merger and not tendered in the Tender Offer were converted into the right to receive $43.50 in cash per share.
(4) The option vests and becomes exercisable as to 1/4th of the shares on November 27, 2007 and vests and becomes exercisable as to 1/48th of the shares at the end of each full month thereafter.
(5) Pursuant to the terms of the Merger, 739,877 shares under this option were cancelled in exchange for a cash payment to the Reporting Person equal to the difference between the offer price per share of $43.50 and the exercise price per share of the option and the remaining shares under the option were assumed and exchanged for an option to purchase 36,247 shares of HP Common Stock at an exercise price per share of $6.70.
(6) Pursuant to the terms of the Merger, 278,380 shares under this option were cancelled in exchange for a cash payment to the Reporting Person equal to the difference between the offer price per share of $43.50 and the exercise price per share of the option and the remaining shares under the option were assumed and exchanged for an option to purchase 12,290 shares of HP Common Stock at an exercise price per share of $6.70.
(7) The option vests and becomes exercisable as to 1/4th of the shares on May 1, 2009 and vests and becomes exercisable as to 1/48th of the shares at the end of each full month thereafter.
(8) Pursuant to the terms of the Merger, 27,980 shares under this option were cancelled in exchange for a cash payment to the Reporting Person equal to the difference between the offer price per share of $43.50 and the exercise price per share of the option and the remaining shares under the option were assumed and exchanged for an option to purchase 18,615 shares of HP Common Stock at an exercise price per share of $8.38.
(9) The option vests and becomes exercisable as 1/72nd of the shares at the end of each full month after October 1, 2008.
(10) Pursuant to the terms of the Merger, 66,666 shares under this option were cancelled in exchange for a cash payment to the Reporting Person equal to the difference between the offer price per share of $43.50 and the exercise price per share of the option and the remaining shares under the option were assumed and exchanged for an option to purchase 135,388 shares of HP Common Stock at an exercise price per share of $7.65.
(11) The option vests and becomes exercisable as to 1/4th of the shares on October 1, 2009 and vests and becomes exercisable as to 1/48th of the shares at the end of each full month thereafter.
(12) Pursuant to the terms of the Merger, 100,000 shares under this option were cancelled in exchange for a cash payment to the Reporting Person equal to the difference between the offer price per share of $43.50 and the exercise price per share of the option and the remaining shares under the option were assumed and exchanged for an option to purchase 101,540 shares of HP Common Stock at an exercise price per share of $7.65.
(13) The option vests and becomes exercisable as to 1/4th of the shares on May 1, 2010 and vests and becomes exercisable as to 1/48th of the shares at the end of each full month thereafter.
(14) Pursuant to the terms of the Merger, 44,270 shares under this option were cancelled in exchange for a cash payment to the Reporting Person equal to the difference between the offer price per share of $43.50 and the exercise price per share of the option and the remaining shares under the option were assumed and exchanged for an option to purchase 81,973 shares of HP Common Stock at an exercise price per share of $17.73.
(15) The option vests and becomes exercisable as to 1/4th of the shares on May 1, 2011 and vests and becomes exercisable as to 1/48th of the shares at the end of each full month thereafter.
(16) Pursuant to the terms of the Merger, this option was assumed and exchanged for an option to purchase 133,525 shares of HP Common Stock at an exercise price per share of $21.31.

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