In November 2008 Microsoft announced plans for Microsoft Security Essentials code named Morro. In June a beta version of Microsoft Security Essentials was officially announced on the Microsoft Malware Protection Center team blog for up to 75,000 individuals.
Qouting the team blog "Microsoft Security Essentials is a new, no-cost, anti-malware solution for genuine Windows PC consumers that provides real-time protection against viruses, spyware and other malicious threats. It is a lightweight, effective and modern anti-malware which runs on 32 bit and 64 bit Windows 7, Windows Vista and Windows XP SP2 and higher, and on modern consumer form-factors such as netbooks."
The beta release is currently only available only to customers in the United States, Israel (English only), People's Republic of China (Simplified Chinese only) and Brazil (Brazilian Portuguese only).
Visit the Microsoft Security Essentials Website for further information and check back regularly for updates.
For more free software and services check out the BlogMS resource guide to Microsoft Free Software and Online Software.