>It didnt find anything because either:
>
>1) The MS app is beta and still has a lot of dev work to go vs. other long established players, or
>
>2) There was nothing and SpyBot was mistaken.

I've recently read a comparison test of several spy catcher apps, and M$ fared the worst. Not one of them caught all, but most of the reputable apps caught between 50 and 80% of the stuff.
The authors' recommendation is to have two of them installed, so what one passes the other will catch - and don't count M$ there, it catches about 20-30% of what others do. So, it's rather your first option.