MICROSOFT SECURITY ESSENTIALS
System Requirements: 
- Operating System: Windows XP Service Pack 3 [SP3]*; Windows Vista [Service Pack 1, or Service Pack 2]*; Windows 7*
 - For Windows XP, a PC with a CPU clock speed of 500 MHz or higher, and 256 MB RAM or higher.
 - For Windows Vista and Windows 7, a PC with a CPU clock speed of 1.0 GHz or higher, and 1 GB RAM or higher.
 - VGA display of 800 × 600 or higher.
 - 200 MB of available hard disk space.
 - An Internet connection is required for installation and to download the latest virus and spyware definitions for Microsoft Security Essentials.
 - Internet Browser:
 
- Windows Internet Explorer 6.0 or later.
 - Mozilla Firefox 2.0 or later.
 
- Microsoft Security Essentials also supports Windows XP Mode in Windows 7.For more information see the system requirements for Windows XP Mode in Windows 7.
 
*Your PC must run genuine Windows to install Microsoft Security Essentials. Internet access fees may apply while downloading. 
New Features 
- Automatic malware remediation for enhanced protection
 - Performance enhancements
 - Simplified UI to make it easier to use
 - New and improved protection engine for better security