Which file type can be used to execute code in Excel without issuing a warning about opening a macro-supporting file type?

XLTM is the macro-enabled template format for Excel, and in certain Office configurations it avoids the Protected View or macro-enable warning that XLSM files generate because Excel treats template file types under different trust and opening logic. Attackers exploit this distinction to embed malicious VBA code in XLTM files and deliver them via phishing, where the code executes silently without the expected security dialog alerting the victim.

CSV files are plain-text comma-separated value files with no support for macros, VBA, or any form of executable code.

XLSB (Excel Binary Workbook) can contain macros but still triggers Office security warnings when opened, so it does not bypass the macro warning the way XLTM can.

PRN files are printer-formatted text output files and have no capability to store or execute macros or embedded code.