Microsoft has released Microsoft Security Essentials public Beta
1.0.1407.00, a free security software for your PC. With Microsoft
Security Essentials you can protect your PC from various factors like
viruses and spyware, including Trojans,worms and other malicious
software.

Its very easy to install and use. Updates are automatic, you don’t have to worry about latest protection.
Requirement:
· For XP - CPU with clock speed of 500 MHz or higher
· For XP - Memory: 256 MB RAM or higher
· For Vista / W7 - CPU with clock speed of 1.0 GHz or higher
· For Vista / W7 - Memory: 1 GB RAM or higher
· VGA (Display): 800 x 600 or higher
· Storage: 140 MB of available hard-disk space
·
An Internet connection is required for installation and to download the
latest virus and spyware definitions for Microsoft Microsoft Security
Essentials
Its available for only first 75,000 users but Microsoft can increase the limit if required. So grab your copy asap.
You’ll need a Windows Live ID and will have to fill a small survey before downloading it. Its available on Microsoft Connect.