Windows® Defender
Windows Defender 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 minimizes interruptions and helps you stay productive. Now with 2 free support incidents for Windows XP and Windows Server 2003.
  • Spyware detection.
  • Straightforward operation and thorough removal technology.
  • Scheduled scanning and removal.
  • Improves Internet browsing safety
  • Helps stop spyware before it infiltrates your computer.
    Runs in the background and automatically handles spyware based on preferences that you set.
  • Auto updates
More Info: Homepage

Download: Windows® Defender | Windows® Defender x64 version