Microsoft started out so good with releasing a free AV. At first I've used it and saw good reviews about it; it was in the top 5 or so for AV. Then 3 months later you see reports that it's "not that good, but sufficient". And now you see reports that it scores LAST on a trojan which steals users' banking information.
It just shows that MS doesn't care about giving away stuff for free. They care about the benjamins, nothing more nothing less.