Microsoft Knowledge Base Article 892279 contains the following summary:
Microsoft has released a beta version of Microsoft Windows AntiSpyware. This beta release is built from technology that was acquired from Giant Company Software. You can use Windows AntiSpyware (Beta) to help detect and remove unwanted software, to help prevent its installation, and to help you see what software is running on any computer that is running Windows AntiSpyware (Beta). Together with security technologies in Microsoft Windows XP Service Pack 2 that help improve the security of browsing, Windows AntiSpyware (Beta) will help protect customers on the Internet.