Windows Defender is antispyware software that's included with Windows and runs automatically when it's turned on. Using antispyware software can help protect your computer against spyware and other potentially unwanted software. Spyware can be installed on your computer without your knowledge any time you connect to the Internet, and it can infect your computer when you install some programs using a CD, DVD, or other removable media. Spyware can also be programmed to run at unexpected times, not just when it's installed.
Windows Defender offers two ways to help keep spyware from infecting your computer:
Real-time protection. Windows Defender alerts you when spyware attempts to install itself or to run on your computer. It also alerts you when programs attempt to change important Windows settings.
Scanning options. You can use Windows Defender to scan for spyware that might be installed on your computer, to schedule scans on a regular basis, and to automatically remove anything that's 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 alert you to potential risks if it determines that software detected is spyware or other potentially unwanted software. To help keep your definitions up to date, Windows Defender works with Windows Update to automatically install new definitions as they're released. You can also set Windows Defender to check online for updated definitions before scanning. For information about keeping your definitions up to date and how to manually download the latest definitions, see Keep Windows Defender definitions up to date.
Open Windows Defender by clicking the Start button . In the search box, type Defender, and then, in the list of results, click Windows Defender.
Click these links for more information about using Windows Defender:
Scan for spyware and other potentially unwanted software
Understanding Windows Defender alert levels
Understanding Windows Defender real-time protection