Article ID: 976098 - Last Review: October 7, 2011 - Revision: 4.0

December 2009 cumulative time zone update for Microsoft Windows operating systems

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This update supersedes and replaces update 970653, which was released in August 2009. This update also includes additional time zone changes that were signed in to law after update 970653 was created.

If you have already deployed update 970653, read the descriptions of the specific time zone changes that are addressed in this article to determine whether you must deploy this update immediately. If systems are not directly affected, you can schedule deployment at the next available opportunity.

We recommend that you deploy the most current Windows cumulative time zone update to guarantee the consistency of the time zone database on all systems.

Before you apply the update that is described in this article, be aware of potential issues that may affect Microsoft Outlook.
For more information about these issues, click the following article number to view the article in the Microsoft Knowledge Base:

931667 (http://support.microsoft.com/kb/931667/ ) How to address the daylight saving time changes in 2007 by using the Time Zone Data Update Tool for Microsoft Office Outlook

Important

If you are running Microsoft Exchange Server in an Information Technology (IT) environment, you must take additional measures to guarantee the correct operation of Exchange Server.

For more information about the Exchange daylight saving time (DST) update, click the following article number to view the article in the Microsoft Knowledge Base:
941018 (http://support.microsoft.com/kb/941018/ ) How to address daylight saving time by using the Exchange Calendar Update Tool
Cumulative time zone updates contain only data that has changed for a specific region or that was added to maintain parity with other operating system versions. Therefore, if a time zone key has been deleted, some original values may not be restored after you apply the cumulative zone update.
We do not recommend that you delete any registry keys that are related to time zones. On a computer that has incomplete time zone keys, first restore the time zone keys from a known good backup. Then, apply the update.

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INTRODUCTION

The update that this article describes changes the time zone data to accommodate daylight saving time (DST) changes in several countries, as outlined in this article. This update also includes other DST-related changes, time zone-related changes, and settings-related changes. Some of these changes have occurred since the products that are listed in the "Applies to" section were originally released.

The update that this article describes is a cumulative update rollup that includes all the changes that were previously released in Microsoft Knowledge Base (KB) articles 928388, 929120, 933360, 942763, 951072, 955839 and 970653.

For more information about how DST changes may affect other Microsoft products, visit the following Microsoft Web site: http://support.microsoft.com/gp/cp_dst (http://support.microsoft.com/gp/cp_dst)

For more information about how daylight saving time changes may affect other Microsoft products, click the following article number to view the article in the Microsoft Knowledge Base:

914387 (http://support.microsoft.com/kb/914387/ ) How to configure daylight saving time for Microsoft Windows operating systems

Note When you apply this update, you may receive the following message:

Update cannot be installed as a newer or same time zone update has already been installed on the system.

This message indicates that you have already applied the correct update or that Windows Updates or Microsoft Update has automatically installed this update. No additional action is required to update the Windows operating system software.

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The following files are available for download from the Microsoft Download Center: