http://www.news.com/2100-1012_3-6224917.html

"David LeBlanc, a senior software development engineer in the Microsoft
Office group, added further details to Microsoft's change of direction.

He wrote on Friday in his blog: "We noticed that attackers seemed to be
preferentially hitting the parsers for the older formats, and if the great
majority of you don't need the older format, it's risk without reward. This
was the thinking behind disabling the older formats by default in Office
2007 and eventually Office 2003 SP3. We'll try harder to make enabling older
formats much more user-friendly in the future."