"posting nearly 5,000 pages of new technical documentation for the Microsoft Office binary file formats for Word, Excel and PowerPoint" Press release: http://www.microsoft.com/presspass/press/2008/jun08/06-30InteropUpdatePR.mspx Technical specs...

The Office security team typically targets memory-corruption bugs in the software like buffer overruns, integer overruns, and format strings... http://www.darkreading.com/document.asp?doc_id=159305