Important: This update supersedes and replaces update 979306, which was released in February 2010. This update also includes additional time zone changes that were signed in to law after update 979306 was created.

If you have already deployed update 979306, 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 How to address time zone changes by using the Time Zone Data Update Tool for Microsoft Office Outlook
  • 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 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 is 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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