Mario, Up through Windows 7 Windows Defender was basically an anti-malware, anti-spyware, anti-PUP program and Microsoft Security Essentials, which you had to intentionally install, was Microsoft's antivirus program. Windows Defender can safely run on any Windows machine prior to Windows 8 that has another third-party antivirus program running. It hurts nothing to let Windows Defender run with antivirus software running on a Windows 7 machine.
Once you get to Windows 8 and beyond, the old Microsoft Security Essentials antivirus function was rolled into the existing prior functions of Windows Defender and the full-function antivirus version of Windows Defender was born. You must absolutely not run Windows Defender in a Win8 or later environment if you choose to use a third-party antivirus. In fact, most third-party antivirus programs check to see if Windows Defender is active on Win8 or Win10 machines when they're being installed and intentionally disable it. One should never, ever, ever, have more than one antivirus program running on a machine at the same time. Brian
