After a fresh install of Virtualmin on a Ubuntu 16.04 system, I went to check the Virtualmin configuration and saw that there was the following error:

LibClamAV Error: cli_loaddbdir(): No supported database files found in /var/lib/clamav

I've seen this before and I had to Google for the solution which I found here.

All you have to do is run the commands below and then try again and everything should work as far as ClamAV is concerned:

sudo service clamav-freshclam stop
sudo freshclam
sudo service clamav-freshclam start

After running those commands, I no longer received the LibClamAV Error because the problem was solved.