MS Office 2007 does not protect/sign the content of the data found in the core.xml file which is part of the data saved whenever MS Office 2007 is asked to save data in OOXML format, this allows attakers to spoof the data found in it - creator name, last modified date, etc - without invalidating the signature of the file.

http://www.securiteam.com/windowsntf...V00A0KKLE.html