MS, today released a new version of the MSE beta, the build number is 1801. This is for people in the ongoing beta program.

1/4/2010: Microsoft has released yet another beta for MSE. the build number is 1901. No visible changes.

Here's the download links.

Windows 7/Vista x64:
http://cid-afe12d66a5ec12fa.skydrive...vista-Win7.exe

Windows 7/Vista x86:
http://cid-afe12d66a5ec12fa.skydrive...vista-Win7.exe

This version(1.0.1801.0) of the Microsoft Security Essentials ongoing beta
contains:

1. An updated validation of genuine windows in the
application
2. Resolution of the signature update issue that impacted PCs that
were offline for extended periods and frequently toggled
between
sleep/hibernation and active mode
3. Some user interface improvements including better scan reports
and clearer messaging around definition updates
4. Other miscellaneous fixes and enhancements

This version of Microsoft Security Essentials will be released
to customers in January/February 2010.