Summary of DATA DOMAIN, INC.

Results of Operations and Financial Condition, Financial Statements and Exhibit

Item 2.02 Results of Operations and Financial Condition

On October 23, 2008, Data Domain, Inc. ("Data Domain") issued a press release announcing its financial results for the quarter ended September 30, 2008. A copy of this press release is furnished as Exhibit 99.1 to this report.

The information in this Item 2.02 and the exhibit attached hereto shall not be deemed "filed" for purposes of Section 18 of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), nor shall it be deemed incorporated by reference in any filing under the Securities Act of 1933, as amended, or the Exchange Act regardless of any general incorporation language in such filing, except as shall be expressly stated by specific reference to this report in such filing.

Use of Non-GAAP Financial Information

Data Domain has supplemented the financial measures contained in the attached press release that are provided in accordance with generally accepted accounting principles ("GAAP") with non-GAAP financial measures. Data Domain believes that these non-GAAP financial measures better reflect its core operating results and thus are appropriate to enhance the overall understanding of its past financial performance and its prospects for the future. These adjustments to Data Domain's GAAP results are made with the intent of providing both management and investors a more complete understanding of Data Domain's underlying operational results and trends and performance. Management uses these non-GAAP measures to evaluate Data Domain's financial results, develop budgets and manage expenditures. The method Data Domain uses to produce non-GAAP financial results may differ from the methods used by other companies. Data Domain's reference to these non-GAAP financial results should be considered in addition to results that are prepared under current accounting standards but should not be considered as a substitute for, or superior to, the financial results that are presented as consistent with GAAP. Reconciliation of the non-GAAP financial measures to the nearest GAAP financial measures is included in the press release attached hereto as Exhibit 99.1.