Windows Defender is your first line of defense against the bad guys. 

Introduced in January of 2005,  Windows Defender is Microsoft’s free anti-spyware application.  It is included free with Windows Vista and Windows 7, and is available as a free download for Windows XP. 

It was announced in December of 2008 that Windows Defender is being discontinued and will be replaced by a new application known as Microsoft Security Essentials (MSSE).  MSSE is currently in Beta release and is expected to be released in November of 2009. 

More info on Windows Defender:
http://www.microsoft.com/windowsxp/using/security/expert/glenn_windefender.mspx

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