AVAST Software's avast! Free Antivirus most certainly deserves to be on any list of the best free antivirus programs. avast! Free Antivirus has fully functioning antivirus and antispyware engines protecting your PC from threats from the Internet, your files, emails, and even instant messages.
avast! Free Antivirus supports Windows 8, Windows 7, Windows Vista, and Windows XP.I personally have been using it on one of my rigs for the past two years no issues thus far.