" If I like to open a BoM with MS Excel, I get a security alert which advises against an opening. Why?"

It is not quite trivial to generate an Excel file if one does not assume a working Excel version to be installed. But we definitely want every user to be able to create an Excel file, even if he has no Excel installed and running.

When loading a file Microsoft does not really check whether it would be dangerous or not. According to our knowledge MS only checks whether the file was created by an Excel version or not. If not, this message pops up. Please ignore the message in this second case.