After analyzing reports of "zero-day" attacks concerning a vulnerability in Excel spreadsheet software, Microsoft has actually discovered that the flaw affects the following products: Microsoft Excel 2003, Excel Viewer 2003, Excel 2002, Excel 2000, Microsoft Excel 2004 for Mac, and Microsoft Excel v. X for Mac.

The vulnerability is a result of the way Excel manages the computer's memory and has prevented the Redmond Company from issuing an update so far but Microsoft officials claim that such a patch is in the works.

Meanwhile Microsoft has offered a number of workarounds for the flaw that could allow for remote code execution. Advanced users can prevent Excel Repair mode by modifying Access Control List to the Excel Resiliency registry key in Excel 2003. They can also block all Excel file types at the E-mail gateway to prevent Excel documents from entering a network and block the ability to open external Excel documents that are e-mail attachments or are hosted on various web sites by removing the registry key that associate the Excel documents with the Excel application.

The average user should limit to not opening or saving Microsoft Excel files if the source of those files is unknown or un-trusted, because opening such a compromised document will result in the exploitation of the vulnerability.