We would like to call out the following fixes included in this rollup:
1) Fix for a security issue which has been assigned a severity rating of critical. More information about the issue can be found in the Microsoft Security Bulletin MS09-003.
2) Fix to allow Internet Explorer 8 to be used for Outlook Web Access (OWA) 2007. This does not include the OWA 2007 S/MIME control. We are still working on some changes in the control to make it work better with Internet Explorer 8. We will be releasing an updated version of the S/MIME control in a future rollup. Users using the S/MIME control should continue to use Internet Explorer 7.
KB 959241 has more details about this release and a complete list of all fixes included in this rollup.
From the installation perspective, a reminder that the rollup installer will overwrite any OWA script files if required to ensure proper operation of OWA. If you have customized the logon.aspx page or other similar OWA pages, you will need to redo any customization after installation of the rollup.
I would also like to address a concern expressed when we announced the release of the rollup last week. Update Rollup 5 for Exchange Server 2007 Service Pack 1 introduced an issue where you receive an error when attempting to enable SCR on a storage group if the environment has a parent domain -> child domain active directory structure. Tim has blogged about this overhere. If you are impacted by this issue, the workaround would be to leave the server which has only the Exchange Server 2007 Management tools installed running Update Rollup 4 for Exchange Server 2007 Service Pack 1 to administer your Exchange organization. An Exchange server which only has the Exchange 2007 Management Tools installed is not vulnerable to the security issue fixed in this bulletin. When the fix is released the server can be upgraded directly to that rollup as our rollups are cumulative.
Finally, I would like to highlight a new "Exchange Software Updates" forum at http://social.technet.microsoft.com/Forums/en-US/exchangesoftwareupdate/threads/ which deals with Updates we release for Exchange. If you encounter issues, post them in the Exchange Software Updates forum as opposed to comments in response to this blog. We have staffed the forums with engineers monitoring the forum ready to assist you unlike the blog comments which are usually blocked till I or another person on my team can take a look and respond.