I just read or heard that
Security Essentials failed certification /again/. I've stopped using it and stopped recommending it. You'd think, like I guess I did, that if anyone would know Windows best it'd be them. Apparently I was wrong! Pretty bad when I refuse to use something free! Anyway, I moved to bit defender's free version. It's light like SE, but actually does a pretty good job.
Just FYI, and use what you'd like!