Few weeks back Microsoft announced the beta release of Microsoft Security Essentials and offered users to become testers. But in case if anybody missed that oppurunity then still there is a chance to be tester of MSE. Microsoft is still accepting the enteries for the beta testing of MSE.
Build no 1.0.1611.0 of MSE was released in September, which is available on MSE official website for download. And its later beta build 1.0.1676.0, that updates to 1.0.1743.0 is available for download for testing purpose at Microsoft Connect.
If any body intersted in going for this beta build then they can easily apply by foolowing the given link below and it will be auto accepted.