A macro virus is a type of computer virus that could be stored in macros within an Microsoft Office file (such as a document, presentation, workbook, or template), or within any ActiveX control, COM add-in, or Office add-in. We refer to macros, ActiveX controls, and add-ins as "Active content".

Microsoft Office files that have a macro in them have a different file extension to indicate that they have an embedded macro. For example, a normal modern Word document is a .DOCX file, but if a macro added to the file it's saved as a .DOCM file. Likewise, a modern Excel workbook is a .XLSX file, and a modern PowerPoint presentation is a PPTX file, but if there are macros in them the Excel file becomes a .XLSM file and the PowerPoint presentation becomes a .PPTM file.

For your protection, Office doesn't run active content automatically unless the file has been marked as a trusted document or opened from a trusted location.

Notes: 

For all other files containing a macro or other active content you'll usually see a message that looks like this:

The Message Bar

Do not select Enable Content unless you're certain that you know exactly what that active content does, even if the file appears to come from a person or organization that you trust.

Note: Opening a file with macros disabled might limit the file's expected functionality.

Office can't scan files or locations to find and delete macro viruses, however all modern anti-malware software - like Microsoft Defender Antivirus - should be able to detect, and block, known macro viruses.

See Also

Enable or disable macros in Office files

Change macro security settings in Excel

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