“Since implementing the Data Domain Restorer we have retired the six DLT tape drives and the 126 tapes used to back-up our data stores. We now rely on the Restorer for all our back up and restore needs.” — Ned Rendell
MIS Director
Mohler, Nixon & Williams

Press Release

Data Domain Announces Exercise and Closing of Overallotment Option

SANTA CLARA, Calif. — December 3, 2007 —Data Domain, Inc. (NASDAQ: DDUP) announced today that the underwriters of its previously announced public offering have exercised their over-allotment option to purchase an additional 538,101 shares of the company's common stock at a price of $27.00 per share, less the applicable underwriting discount. The closing of the additional purchase took place today. Of the shares sold pursuant to the exercise of the over-allotment option, 251,114 shares were sold by Data Domain, Inc., and 286,987 shares were sold by the selling stockholders identified in the prospectus. Data Domain will not receive any of the proceeds from the sale of the shares sold by the selling stockholders. The sale of the over-allotment shares by the company brings the total number of shares sold by the company in the offering to 3,051,114, and the total net proceeds to the company in the offering to approximately $78.0 million.

Morgan Stanley acted as book-running manager for the offering and Pacific Crest Securities, Wachovia Securities, Canaccord Adams Inc. and Needham & Company, LLC acted as co-managers. A registration statement relating to the offering was filed with and declared effective by the Securities and Exchange Commission. The offering of the common stock may be made only by means of a prospectus, copies of which may be obtained from Morgan Stanley & Co. Incorporated, 180 Varick Street, New York, New York 10014, Attention: Prospectus Department, by calling 1-866-718-1649 or by emailing prospectus@morganstanley.com.

This press release shall not constitute an offer to sell or the solicitation of an offer to buy, nor shall there be any sale of these securities in any state or jurisdiction in which such offer, solicitation or sale would be unlawful prior to registration or qualification under the securities laws of any such state or jurisdiction.

Data Domain and the Data Domain logo are trademarks or registered trademarks of Data Domain, Inc. All other trademarks used or mentioned herein belong to their respective owners.

Contact Information

Data Domain

Michael P. Scarpelli
Chief Financial Officer
408.980.4800
ir@datadomain.com