Spyware Confidential concluded that Windows Defender detected and removed approximately 65% to 75% of the spyware compared to SpywareDoctor and SpySweeper. Windows Defender left behind quite a few registry keys. It did better with file removal than with registry clean up. WD failed to remove some spyware that initiated the download of AdwareSheriff when I reconnected the vm to the internet.
Beside, Spyware Confidential also found annoying feature that even though real time protection features is turned off, Windows Defender still tries periodically to add a new task to the Windows Task Scheduler for a daily scan. And also, there is no way to check for updates from within Windows Defender program, all updates is done via Windows Updates.
Check out more reviews of Windows Defender.