Hi, Till, thanks for your response.
Plesk has never been installed on this server, but ISPConfig is configured to use the same port that Plesk uses (8443). This is probably why the probing software thought that the server is running Plesk.
What you say regarding the file path translation makes sense.
It sounds like I can ignore these probes, as they will never be successful if they're looking for Plesk.
Thanks again for the thorough explanation!