On Nov'9th, Microsoft began pushing out a "beta refresh" of Microsoft Security Essentials build 2.0.522.0 via Windows Update. It's said to be the Release Candidate build, but Microsoft officials aren't calling it that publicly.
Microsoft delivered the beta 2 of MSE in July 2010, and at that time, it was said the new version include "Windows Firewall integration" and more. Sorry! but no firewall feature is added to new build.
A new Knowledge Base article KB2461287 describes the refresh includes "improvements to quality of the product including performance enhancements as well as some user interface modifications." The product team has removed the protection against web threats feature in the Security Essentials Beta "as it was causing PC performance issues."
According to WinRumors, Microsoft also added a mechanisms to help thwart Windows 7 activation-bypass hacks. If users running new MSE on their Win7 PCs cann't pass Genuine validation and don't resolve the issue, after 30 days, MSE will be disabled.