Software Tool : Clamav 0.103.1 Antivirus
License : Open Source 
Site : ClamavNet

Clamav is free opensource antivirus for detection of trojans, viruses, malware & other malicious threats. ClamAV antivirus automatically does signature updates to detect newest threat to your system. Consists multi-threaded scanner daemon for efficient work flow and command line functions for file scanning.

(goes to author site, so choose your download as per your need)