According to Computerworld, Microsoft plans to boost the security of older versions of Office by backporting an Office 2010 security feature. The article explains:
Dubbed Office File Validation (OVE), the technology validates older, pre-XML file formats for Word, Excel, PowerPoint and Publisher, then opens those that don’t conform to the documented format – rigged files containing an exploit, for example – in a special ‘sandbox’ within Office 2010 called Protected View.
However, instead of opening suspicious files in a sandbox, OVE in Office 2003 and 2007 will prompt a warning that the document could be dangerous. The optional update will be available in the first quarter of 2011.