http://securitywatch.pcmag.com/security-software/320162-free-antivirus-products-rule-the-world

QUOTE: Researchers found that 23.0 percent use a Microsoft product, 15.9 percent rely on avast!, and 8.9 percent run AVG.  Microsoft still leads, with over 25 percent of installations. Present on nearly 15 percent of surveyed systems, Malwarebytes is a surprise winner of second place. Note that the basic Malwarebytes Anti-Malware doesn’t include real-time protection. Looking at individual products rather than companies, the top five were: Microsoft Security Essentials, avast! Free Antivirus 2014, Windows Defender (a component of Windows 7 and Windows 8), Avira Free AntiVirus (2014), and AVG AntiVirus FREE 2014. Yet again, free products rule.