Taking XLSM File Precautions Before trying to open an XLSM file, Kaspersky warns that some macros in these files can be malicious, especially if you receive your spreadsheet through a random email.

When you open macro-enabled workbooks, which are Excel files with an XLSM extension, Microsoft Office alerts you with a security warning.

Excel failed to warn the user before running any macro contained in a file in the SYLK file format, an almost-forgotten file type but one with which Microsoft Office had maintained compatibility.

Microsoft will block downloaded macros in Office versions going back to 2013 Enabling macros for these files will be possible but more difficult than before.