Defend your computer against viruses, spyware, and other malware
Microsoft Security Essentials is a free download for Windows 7 that helps protect your computer from viruses, spyware, worms, Trojans, and other malware. For more information, see
Help protect your PC with Microsoft Security Essentials.
https://www.microsoft.com/en-us/safety/pc-security/microsoft-security-essentials.aspx
Windows 7 also includes Windows Defender, software that helps protect your computer from pop-up ads, slow performance, and security threats caused by spyware and other unwanted software. For more information, see Using Windows Defender.
Note: In Windows 8, Windows Defender replaces Microsoft Security Essentials. Windows Defender runs in the background and notifies you when you need to take specific action. However, you can use it anytime to scan for malware if your computer isn’t working properly or you clicked a suspicious link online or in an email message.