ClamAV is a virus detector created prior to 2005.
Unlike its equivalents in the Windows world, it is not used to protect the machine on which it is installed, but rather to scan the files stored on it. For example, it is often used on web servers, file servers and mail servers. ClamAV can detect a large number of threats on any operating system. Signature updates, sustained by a very involved community, can be accessed free of charge.
ClamAV is available under the GPL v2.
The antivirus engine is the library libclamav, written in C.
This solution does not have any opinions yet