Mailing the story:

ClamAV is an open-source and free antivirus software toolkit able to detect many types of malicious software, including viruses, trojans, malware, adware, rootkits, and other malicious threats. One of its main uses of ClamAV is on mail servers as a server-side email virus scanner or used on file hosting servers to periodically scan to make sure files are clean, especially if the public can upload to the server.