Here you can find a tutorial about pfSense and HAVP: https://turbofuture.com/internet/How-to-Set-Up-an-HTTP-Anti-Virus-Proxy-Using-pfSense-and-HAVP/
There is also a german installation video on youtube: https://www.youtube.com/watch?v=7JooGhunk0s
ClamAV® is an open source antivirus engine for detecting trojans, viruses, malware & other malicious threats. http://www.clamav.net/