This program helps protect Windows Vista against pop-up ads, slow performance, and security threats due to spyware, adware, keyloggers and other unwanted software. Windows Defender monitors in real-time protected areas within the Windows Vista operating system that unwanted software targets, such as the Startup folder and Autorun entries in the registry. When a program tries to modify a protected area or function in Windows Vista, Windows Defender prompts the user to either allow or reject the change in an effort to guard against unwanted installation of software or operating system modifications. Windows Defender is enabled by default and uses signature updates to keep up with the latest attacks. It is thus not as robust as antivirus software that uses behavioral modeling as well as signatures to detect malicious software, however. Windows Defender is thus intended to serve as a complement to already installed third-party antivirus software. Note that Windows Defender is also available as a download for Windows XP or Windows Server 2003, and it performs the same functions as in Windows Vista.