It's important to run antispyware software whenever you're using your computer. Spyware and other potentially unwanted software can try to install itself on your computer any time you connect to the Internet. It can also infect your computer when you install some programs using a CD, DVD, or other removable media. Spyware or potentially unwanted software can also be programmed to run at unexpected times, not just when it is installed.

Windows Defender offers three ways to help keep spyware and other potentially unwanted software from infecting your computer:

  • Real-time protection.‍‍ Windows Defender alerts you when spyware or potentially unwanted software attempts to install itself or to run on your computer. It also alerts you when programs attempt to change important Windows settings.

  • SpyNet community. The online Microsoft SpyNet community helps you see how other people respond to software that has not yet been classified for risks. Seeing if other members of the community allow software can help you choose whether to allow it on your computer. In turn, if you participate, your choices are added to the community ratings to help other people choose what to do.

  • Scanning options. You can use Windows Defender to scan for spyware and other potentially unwanted software that might be installed on your computer, to schedule scans on a regular basis, and to automatically remove anything that is detected during a scan.

When you use Windows Defender, it's important to have up-to-date definitions. Definitions are files that act like an ever-growing encyclopedia of potential software threats. Windows Defender uses definitions to determine if software that it detects is spyware or other potentially unwanted software, and then to alert you to potential risks. To help keep your definitions up to date, Windows Defender works with Windows Update to automatically install new definitions as they are released. You can also set Windows Defender to check online for updated definitions before scanning.