The Microsoft Security Essentials (MSE) Ongoing Beta Program has started letting testers in and is already handing out build 1.0.1676.0. MSE is so far available in 39 markets.
Full Story: http://arstechnica.com/microsoft/news/2009/10/microsoft-security-essentials-ongoing-beta-begins.ars
Full Story: http://arstechnica.com/microsoft/news/2009/10/microsoft-security-essentials-ongoing-beta-begins.ars