On Debian and Windows I use ClamAV which is maintained by Cisco systems.

https://www.clamav.net/
https://www.clamav.net/downloads

It comes packaged with Debian and other GNU/Linux distributions, and I've used it on OpenBSD. On windows I use the Windows defender suite but this also works on windows through an admin CMD command line. You download the package from the above link and install it. Then you need to edit two config files in the directory "C:\Program Files\ClamAV\conf_examples\". Copy these files to the main directory

 
C:\> copy "C:\Program Files\ClamAV\conf_examples\*.sample" .. 
C:\> cd "C:\Program Files\ClamAV\" 
C:\> move clamd.conf.sample clamd.conf
C:\> move freshclam.conf.sample freshclam.conf
C:\> notepad clamd.conf

#Comment or remove the line below.
#Example

Save and close the file, then do the same for freshclam.conf

C:\> notepad freshclam.conf

# Comment or remove the line below.
#Example

Save and close the file after commenting Example with #

C:\> freshclam