Microsoft Security Essentials
Microsoft Security Essentials, which was initially known as Morro, is a free antivirus application provided by Microsoft for its operating systems Windows XP, Windows Vista and Windows 7. It was built to replace the previous antivirus software created by Microsoft, Windows Live OneCare, which required payment. As Microsoft Security Essentials is offered for free, it has an extensive user base. It is also lightweight and speedy, which makes it very useful. As it offers tight integration with the Windows environment, it disables Windows Defender, and provides much more extensive protection from malware, spyware, viruses and rootkits.
http://windows.microsoft.com/en-US/windows/products/security-essentialsTags: MICROSOFT, Microsoft Security Essentials, Windows Defender, Windows Live OneCare, Windows Vista