You don’t need to install more than one antivirus program. In fact, running more than one antivirus program at the same time can cause conflicts and errors that make your antivirus protection less effective or not effective at all.
Windows 7 and Windows Vista include spyware protection called Windows Defender. To help fight both viruses and spyware, you can download Microsoft Security Essentials at no cost. If you download Microsoft Security Essentials, Windows Defender will be disabled automatically. Make sure to uninstall any other antivirus software (whether you installed it or it came preinstalled) on your computer first.
Windows 8 includes antivirus and antispyware protection called Windows Defender. Windows Defender for Windows 8 replaces Microsoft Security Essentials. It runs in the background and notifies you when you need to take specific action. If you install a different antivirus program, Windows Defender will be disabled automatically.
Note: You might see a warning that Microsoft Security Essentials has been turned off because you have other antivirus software on your computer that automatically turns off Microsoft Security Essentials. This type of warning could also be a fake virus alert that attempts to fool you into downloading malicious software. For examples of such rogue security software, see our Real vs. Rogue Facebook app.
For more information, see How to boost your malware defense and protect your PC.