A security warning appears after the execution of a file that was loaded directly from outlook-stuff.com (without saving).

It is a dialog as shown beneath:

Files that are loaded directly from the internet are classified as risky from the Internet Explorer. That's why this dialog pops up.

The Unknown Publisher in this case is EDV-Service Marchert. So you can execute the file without hesitation. Please see also FAQ Do add-ins from outlook-stuff.com contain malware or similar?.

This security warning cann be "changed" in a simple information popup if the editor buys a certificate and with that purchase signs the software. Authorized certification companies are for example VeriSign or thawte. Due to cost reasons we surrender to purchase such a certificate and we are not planning to use one in future.

The same warning appears (now from the OS) if a file, that has been downloaded from the internet, is saved in a NTFS-file system and then executed:

The reason for that is the same reason mentioned above. You can permanently avoid this message if you uncheck the box next to  Always ask before opening this file or click with the right mouse button onto the file, open the dialogue Properties and then press the button Unblock.