There are many free anti-virus software programs available, and it can be difficult to determine which one is best. Generally speaking, Avast, AVG, and Avira are all popular options that offer good protection against viruses and malware. Additionally, Windows Defender is a free anti-virus program that is included with Windows 10, and provides basic protection against viruses and malware. Ultimately, the best free anti-virus software for you will depend on your specific needs and preferences.