Windows Vista was the first Windows version to include Windows Defender as a built-in antispyware program. Vista shipped with Defender integrated into the operating system, where it could scan for spyware and monitor areas such as startup programs, Internet Explorer add-ons, and security-related settings.
The product’s history began before Vista. Microsoft acquired GIANT Company Software in December 2004 and released a downloadable product called Microsoft AntiSpyware for supported Windows versions, including Windows XP. Microsoft renamed it Windows Defender in late 2005, and the renamed product appeared as a built-in Vista component.
Windows Defender in Vista and Windows 7 primarily addressed spyware rather than functioning as the full antivirus product familiar today. On Windows 7, Microsoft Security Essentials provided broader malware protection and could replace or work alongside Defender. With Windows 8, Microsoft expanded Defender into a more complete antivirus application using technology related to Security Essentials.
The common mistake is answering Windows XP because XP users could download Microsoft AntiSpyware or Defender. XP had access to the product, but Vista was the first release to include it as a standard built-in antispyware feature.