I created Backup of Virtual Server from: Virtualmin > Backup and Restore > Backup Virtual Servers > Backup
After which I got URL to Download the Backup. But when I an navigating to that Download URL I am getting the following error.
I followed the following guide and the file started downloading but the download speed is too low and the file download interrupts and I have to retry downloading it : Warning! Webmin has detected that the program ...
You would get the error message in the screenshot only when the file you wish to download is not accessed via a valid session. You must hit the download link from the same browser window and tab that it is shown. If you do that you should not get the error message that you get.
You get to specify where the backup file is stored on your server if you use an option other than the download in browser option.
Choose a directory on your server and after Virtualmin backup has finished, you can find the archive in that directory and download it from there via FTP or whatever.
It will once you click on the link. Its only a temporary file.
Create a new backup, do not click on the link its creates.
Open a new browser tab and open webmin and file manager and go to that location and you will see it. Delete it after you download the file.