I use MSE in conjunction with McAfee (It came with the PC...I opted for that because it's not as resource intrusive as Norton)
MSE actually caught a couple things that McAfee didn't. WTG MS.
If I have any doubts, I usually go to the free online scan Norton site.
I like this simply because you d/l it, it runs in it's own sandbox and when it's finished, it clears out of your sys without any residuals left.