Malwarebytes - Malwarebytes protects you against malware, ransomware, and other advanced online threats that have made antivirus obsolete and ineffective. Free Anti-Malware & Malware .
Windows Defender - Windows 10 security delivers built-in & ongoing protections you can trust: Windows Defender Antivirus, firewall, family settings, ransomware protection, real-time protection & more. Stay up to date & protected at no extra cost.
Avira - Cloud based email security solution
Microsoft Security Essentials - Microsoft Security Essentials is Microsoft's own foray into the world of virus protection.
Avast! Free Antivirus - Download Avast Free Antivirus on your Windows, Android, and Mac. World-leading antivirus, compatible with all Windows operating systems. Free forever!
Sophos Home - Business-grade cybersecurity for home users