I am no security expert.
However, I have read this article and it is bad news for MSE......
In an interview with Dennis Protection Labs, Holly Stewart, the senior program manager of the Microsoft Malware Protection Center, said that Microsoft Security Essentials was just a “baseline” that’s designed to “always be on the bottom” of antivirus tests. She said Microsoft sees MSE as a first layer of protection and advises Windows users to use a third-party antivirus instead.
I tried it and dumped it after it quit running for no reason a few times. There have been reports all year from mutiple sources that Security Essentials is at the bottom of the list when compared to other AV products. AV Comparatives http://www.av-comparatives.org/ one of the testing groups pulled it's certification months ago. I switched to Avast Free.