Office 2008 12.1.9 update
The Microsoft Office 2008 for Mac 12.1.9 Update improves security. It includes fixes for vulnerabilities that an attacker can use to overwrite the contents of a computer's memory by using malicious code.  The Office 2008 update prepare the suite Microsoft Entourage 2008 for Mac, Web Services Edition that will enable Entourage to connect to servers running Exchange 2007 SP1 or later via the Exchange Web Services format in lieu of WebDAV.  This will improve compatibility, performance, and reliability. The Web Services Edition is expected to be released later this year.  The 12.1.9 update must be installed before Entourage 2008 Web Services Edition is installed.

Applies to: Office 2008, Office 2008 Home and Student Edition, Office 2008 Special Media Edition, Word 2008, Excel 2008, PowerPoint 2008, Entourage 2008

You can read the details and download the update package here.

Office 2004 11.5.5 update
The Office 2004 for Mac 11.5.5 Update contains changes that improve security. Additionally, this update includes fixes for vulnerabilities that an attacker can use to overwrite the contents of a computer's memory by using malicious code.

Applies to: Office 2004 Standard Edition, Office 2004 Student and Teacher Edition, Office 2004 Professional Edition, Word 2004, Excel 2004, PowerPoint 2004, Entourage 2004

You can read the details and download the update package here.

Open XML File Format Converter for Mac 1.0.3
This update improves security. It includes fixes for vulnerabilities that an attacker can use to overwrite the contents of your computer's memory with malicious code.

You can read the details and download the update package here.

What is Office for Mac?
Office for Mac is a suite of Mac-based versions of Microsoft's Office products that run on recent versions of the Mac OS X operating system.  The most recent version is Office 2008 for Mac.  The availability of Office for Mac helps to alleviate Windows Microsoft Office users' concerns about making the switch to Mac.  Note that one does not need to use Office for Mac as Apple sells a suite of productivity applications in the iWork suite.