Microsoft releases free anti-virus software, Security Essentials. It offers real-time protection against viruses, spyware and other malicious programs. Microsoft Security Essentials assured your PC is protected and easy to tell if it is secured. Microsoft says it runs quietly and efficiently in the background so that you are free to use your Windows-based PC the way you want—without interruptions or long computer wait times. You can download the Microsoft Security Essentials for free.