Hackers and scammers sometimes use fake antimalware software to trick you into installing viruses or malware on your computer. Windows Defender is free and is included in Windows, always on and always working to protect your PC against malware. Malware consists of viruses, spyware and other potentially unwanted software. If you’re running Windows 10, Windows 8.1, or Windows 8, you’ve already got Windows Defender built in, helping to protect you against viruses, spyware, and other malware.