Microsoft Antispyware was officially named as Windows Defender in past.  Windows defender beta I was not revealed to general public, but Beta II is now public.  According to Microsoft this is most sophisticated and powerful anti-spyware tool ever build.  Read more about it below,

What is Windows Defender

Windows Defender (Beta 2) is a free program that helps protect your computer against pop-ups, slow performance, and security threats caused by spyware and other unwanted software. It features Real-Time Protection, a monitoring system that recommends actions against spyware when it’s detected, and a new streamlined interface that minimizes interruptions and helps you stay productive.

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