Data Domain, Inc. Reports Restatement of Previously Issued Financial Statements for the Calculation of Net Income (Loss) per Share

Market Wire, October, 2007

Data Domain, Inc. (NASDAQ: DDUP) today announced that in its previously issued financial statements for its fiscal years ended December 31, 2004, 2005 and 2006 and for its fiscal quarters ended March 31, 2006 and 2007 and June 30, 2006 and 2007, it erroneously calculated the weighted average number of shares outstanding for the purpose of determining its net income (loss) per share for each of these periods. The effect of the erroneous calculation was to understate the net loss per share for each of these periods, but in all other respects the Company's financial results and financial condition were not affected by the restatement.

Data Domain intends to file its restated Audited Consolidated Financial Statements for the years ended December 31, 2004, 2005 and 2006 as Exhibit 99.1 to a Current Report on Form 8-K that it intends to file tomorrow, which financial statements may be relied upon by investors.

The previously issued financial statements erroneously included as part of the weighted average number of shares outstanding unvested shares of common stock that were issued pursuant to the early exercise of stock options that were subject to repurchase by the Company at the end of each period. Accordingly, the Company's previously issued financial statements covering such periods should no longer be relied upon because of this error. The effect of this error on each of these periods is as follows:

                            Data Domain, Inc.
                Net Loss per Share Restatement Comparison
                Years ended December 31, 2004, 2005, 2006
                  (in thousands, except per share data)


                                               Year ended December 31,
                                           ===============================
                                             2004       2005       2006
                                           =========  =========  =========


Net loss - as reported                     $  (9,828) $ (13,783) $  (4,026)
                                           =========  =========  =========

Shares used in computing basic and
 diluted net loss per share - as reported      5,559      6,673      7,978

Decrease in weighted average shares
 outstanding                                    (887)      (872)      (850)
                                           ---------  ---------  ---------

Shares used in computing basic and
 diluted net loss per share - as restated      4,672      5,801      7,128
                                           =========  =========  =========


Net loss per share basic and diluted -
 as reported                               $   (1.77) $   (2.07) $   (0.50)

Increase in net loss per share based on
 change in the number of weighted
 average shares outstanding                $   (0.33) $   (0.31) $   (0.06)
                                           ---------  ---------  ---------


Net loss per share basic and diluted -
 as restated                               $   (2.10) $   (2.38) $   (0.56)
                                           =========  =========  =========





                            Data Domain, Inc.
            Net Income (Loss) Per Share Restatement Comparison
          Three months ended March 31, June 30, September 30 and
         December 31, 2006 and March 31 and June 30, 2007 and Six
                   Months Ended June 30, 2006 and 2007
                  (in thousands, except per share data)


                                    Three Months Ended
                ==========================================================
                Mar 31,   Jun 30,   Sept 30,  Dec 31,   Mar 31,   Jun 30,
                  2006      2006      2006      2006      2007      2007
                ========  ========  ========  ========  ========  ========

Net income
 (loss) - as
 reported       $   (749) $     49  $   (934) $ (2,392) $ (1,473) $ (1,231)
                ========  ========  ========  ========  ========  ========

Shares used in
 computing
 basic net
 income (loss)
 per share -
 as reported       7,584     7,757     8,074     8,581     9,560    11,518

Decrease in
 weighted
 average shares
 outstanding      (1,102)   (1,098)   (1,066)   (1,192)   (1,522)   (1,454)
                --------  --------  --------  --------  --------  --------

Shares used in
 computing
 basic net
 income (loss)
 per share -
 as restated       6,482     6,659     7,008     7,389     8,038    10,064
                ========  ========  ========  ========  ========  ========

Net income
 (loss) per
 share, basic -
 as reported    $  (0.10) $   0.01  $  (0.12) $  (0.28) $  (0.15) $  (0.11)

Increase in net
 income (loss)
 per share,
 basic based
 on change in
 the number
 of weighted
 average
 shares
 outstanding    $  (0.02) $      -  $  (0.01) $  (0.04) $  (0.03) $  (0.01)
                --------  --------  --------  --------  --------  --------

Net income
 (loss) per
 share, basic -
 as restated    $  (0.12) $   0.01  $  (0.13) $  (0.32) $  (0.18) $  (0.12)
                ========  ========  ========  ========  ========  ========

Shares used in
 computing
 diluted net
 income (loss)
 per share -
 as reported       7,584    12,283     8,074     8,581     9,560    11,518

Decrease in
 weighted
 average shares
 outstanding      (1,102)   (1,098)   (1,066)   (1,192)   (1,522)   (1,454)
                --------  --------  --------  --------  --------  --------

Shares used in
 computing
 diluted net
 income (loss)
 per share -
 as restated       6,482    11,185     7,008     7,389     8,038    10,064
                ========  ========  ========  ========  ========  ========

Net income
 (loss) per
 share, diluted
 - as reported  $  (0.10) $      -  $  (0.12) $  (0.28) $  (0.15) $  (0.11)

Increase in net
 income (loss)
 per share,
 diluted
 based on
 change in
 the number
 of weighted
 average
 shares
 outstanding    $  (0.02) $      -  $  (0.01) $  (0.04) $  (0.03) $  (0.01)
                --------  --------  --------  --------  --------  --------

Net income
 (loss) per
 share, diluted
 - as restated  $  (0.12) $      -  $  (0.13) $  (0.32) $  (0.18) $  (0.12)
                ========  ========  ========  ========  ========  ========





                 Six months ended
                ========  ========
                Jun 30,   Jun 30,
                  2006      2007
                ========  ========

Net income
 (loss) - as
 reported       $   (700) $ (2,704)
                ========  ========

Shares used in
 computing
 basic net
 income (loss)
 per share -
 as reported       7,734    10,655

Decrease in
 weighted
 average shares
 outstanding      (1,023)   (1,411)
                --------  --------

Shares used in
 computing
 basic net
 income (loss)
 per share -
 as restated       6,711     9,244
                ========  ========

Net income
 (loss) per
 share, basic -
 as reported    $  (0.09) $  (0.25)

Increase in net
 income (loss)
 per share,
 basic based
 on change in
 the number
 of weighted
 average
 shares
 outstanding    $  (0.01) $  (0.04)
                --------  --------

Net income
 (loss) per
 share, basic -
 as restated    $  (0.10) $  (0.29)
                ========  ========

Shares used in
 computing
 diluted net
 income (loss)
 per share -
 as reported       7,734    10,655

Decrease in
 weighted
 average shares
 outstanding      (1,023)   (1,411)
                --------  --------

Shares used in
 computing
 diluted net
 income (loss)
 per share -
 as restated       6,711     9,244
                ========  ========

Net income
 (loss) per
 share, diluted
 - as reported  $  (0.09) $  (0.25)

Increase in net
 income (loss)
 per share,
 diluted based
 on change in
 the number
 of weighted
 average
 shares
 outstanding    $  (0.01) $  (0.04)
                --------  --------

Net income
 (loss) per
 share, diluted
 - as restated  $  (0.10) $  (0.29)
                ========  ========