May As Well Fire-Proof A Paper house
MS Office is vulnerable because it is a cobbled-together collection of products with "interoperability" pasting them together in the illusion of a single product. The paths to hack the products are the same as the paths to use them together. Add to that the crumbling foundation of Windows upon which most installations of Office are built, and you have a tinderbox. Until MSFT limit interoperation and disgorge the registry, their products will be easy targets for firebugs.