Depending on which operating system your computer is running, you can use either Windows Defender or Microsoft Security Essentials to get rid of malicious software and viruses.
If your computer is running Windows 8, you can use the built-in Windows Defender to help you get rid of viruses, spyware, or other malware. If your computer is running Windows 7, Windows Vista, or Windows XP, Windows Defender only removes spyware. To get rid of viruses and other malware, including spyware, on Windows 7, Windows Vista, and Windows XP, you can download Microsoft Security Essentials for free.
In Windows 8, Windows Defender replaces Microsoft Security Essentials
You canít use Microsoft Security Essentials with Windows 8 or Windows RT, but you donít need to because Windows Defender already provides built-in protection.