If i remember it right, the Anti Virus is not working at the moment. After Update to Squid 3.5 and ubguard it doesent work. i hope it comes back again.
CentOS 7.3 brings Squid 3.5 which is not compatibile with current implementation of web antivirus (C-ICAP + Squidclamav), thus in this release nethserver-squidclamav has been removed. We are working to find a suitable replacement for the next release.