Moodle has supported ClamAV from the era of Moodle 1.3 and by default, ClamAV was the only antivirus tool available for Moodle sites. In Moodle 3.1, a new plugin type is added to incorporate external Antivirus plugins developer by different service providers (see our previous coverage over the Moodle Tracker issue here.)
The Antivirus plugin implements the virus scanning functionality in Moodle. The new type of plugins will allow the external contributors to develop plugins for different antivirus products and extend existing antivirus functionality to different areas of Moodle. By default, ClamAV will be available in Moodle core as antivirus tool.
You can refer to the developer docs available in Moodle docs here for examples about Antivirus plugin type and related file structure to be followed.
This addition of new plugin type will result in eliminating the scalability issues in the current ClamAV setup and allow external contributors to design plugins for other antivirus products.
What are the other Antivirus services apart from ClamAV which you would like to see working with Moodle? Do let us know in the comments below.