Microsoft said hackers have found a way to use some older versions of its Excel spreadsheet program to take over control of people's computers.
Microsoft said late Tuesday that it is investigating reports of such attacks, but has not yet determined whether it will patch the hole, or when.
(Msnbc.com is a Microsoft-NBC Universal joint venture.)
People who open a specially crafted Excel file from an e-mail attachment or visit a compromised Web site could be inviting hackers to take over their PCs for malicious purposes such as stealing passwords and other personal information, or sending out spam. Microsoft Office Excel 2003 Service Pack 2, Excel Viewer 2003, Excel 2002, Excel 2000 and Excel 2004 for Mac all contain the security hole.
The software maker said in a statement that users of these programs can protect their computers by using a tool that scans the files for bad code before opening, called Microsoft Office Isolated Conversion Environment.
The most recent versions of the spreadsheet program, Excel 2007, Excel 2007 SP 1 and Excel 2008 for Mac, are not thought to be affected, Microsoft said.