This update fixes vulnerabilities in Office 2011 that an attacker can use to overwrite the contents of your computer’s memory with malicious code. For more information, see the security bulletin that was listed earlier in this document.
Stability is improved.
This update fixes an issue that causes Office 2011 applications to close unexpectedly when you open or use Office 2011 applications.
Alt Text authoring is included.
This update enables the authoring of Alt Text for objects, such as shapes, pictures, tables, charts, SmartArt, and movies in Office 2011 applications.
Before you install the Office for Mac 2011 SP1 Update, make sure that your computer is running Mac OS X v10.5.8 or a later version of the Mac OS X operating system.
You check update via Office by clicking on Help –> Check for Updates or use following link to download it :-