Microsoft plugged more than a few vulnerabilities in Excel last week, but the trade off may be calculation errors.
Microsoft's Bill Sisk said in a post late Friday following the software giant's latest patch batch:
I wanted to let you know that we have updated bulletin MS08-014 to provide additional information on a newly identified issue that causes Microsoft Excel 2003 calculations to return an incorrect result when a Real Time Data source is used. The issue affects a specific scenario and may not affect you. Please see the bulletin for additional details.
Microsoft's bulletin adds the following:
The problem causes Excel calculations to return an incorrect result when a Real Time Data source is used in a user-defined Visual Basic for Applications function. If you have applications that leverage Real Time Data sources in Visual Basic for Applications functions, we recommend that you perform additional testing before initiating a wide deployment of the update.
This KnowledgeBase article has more on the problem and workarounds. Also see Computerworld.