ClamAV is an excellent antivirus able to compete with the more famous commercial antivirus. It is open source and completely free, developed for Linux, Windows and Mac.
The characteristics of ClamAV are those of a common antivirus: it searches for files with viruses, trojans, and general malware, and it is ideal for scanning e-mail attachments or for use with third party programs like Samba or mail servers.
The core of ClamAV is in the libraries that provide detection mechanisms such as compression and decompression of files and support archives, and has also included a smart tool that automatically updates from the internet their “virus definitions,” and that can be integrated with the operating system to control a particular file on the fly.
Its open nature allows it to be integrated and interact with other programs in order to be used as an anti-virus on a mail server or a file server or to run a check directly to the specified files.
The program is passing the buck in a completely free way from the official website!
The difference between ClamAV from all the other antivirus programs is the ability to have a database updated almost in real-time on all of the present threats on the web. This is possible thanks to a community composed of users that automatically report every new threat found during a system scan. The more users there are, the more complete the database will be and the protection will be better.
Reaching a certain number of users, ClamAV will surely become the definitive antivirus!