>and make sure user www-data has at least read and execute permissions

If www-data didn't have r/w access to that directory, my site would be broken!

From the (redacted) comand output I copied above:
>> root@arquivos0:/var/www# sudo -u clamav ls nc_data/
>> [correct directory contents listed]

I do normally mount /var noexec, however I had to remount it exec when I ran dpkg-reconfigure, so that's not it. I've just tested it with /tmp also mounted exec, however that still didn't fix the problem.

> Apparmor/SE Linux is another possibility.

Neither are installed on this server.

BTW, I'm running Ubuntu 16.04 & ClamAV 0.100.2/25075/Mon.

Doug