Security Advisory Affecting Exchange: 2749655
Today Microsoft released Security Advisory 2749655, Compatibility Issues Affecting Signed Microsoft Binaries. I encourage you to read the security advisory. We also saw that Exchange team post the following blog entry Re-released Exchange 2010 and Exchange 2007 update rollups. Microsoft re-released the rollups in order to ensure that third party programs are not impacted by the security advisory.
That is, Microsoft re-released the updates as a pre-emptive measure - just in case.
If you have installed the security advisory, you really don't need to re-install the updates. Quoting from the security advisory:
What does this update do?
This update will help to ensure the continued functionality of all software that was signed with a specific certificate that did not use a timestamp Enhanced Key Usage (EKU) extension. To extend their functionality, WinVerifyTrust will ignore the lack of a timestamp EKU for these specific X.509 signatures.
Note regarding the impact of not installing a rereleased update
Customers who installed the original updates are protected from the vulnerabilities addressed by the updates. However, because improperly signed files, such as executable images, would not be considered correctly signed after the expiration of the CodeSign certificate used in the signing process of the original updates, Microsoft Update may not install some security updates after the expiration date. Other effects include, for example, that an application installer may display an error message. Third-party application whitelisting solutions may also be impacted. Installing the rereleased updates remediates the issue for the affected updates.
Long story short - Microsoft has released the updates "just in case".
Given that Exchange 2010 SP2 Update Rollups can take upwards of an hour to install and your Exchange server is offline while you doing the installation - you may just want to wait for the next UR.
Please note: the Exchange 2010 SP2 UR4 re-release does include one new patch. You can install that separately in a very short timeframe: Outlook only returns one result after you click the "Your search returned a large number of results. Narrow your search, or click here to view all results" message.