Microsoft has partnered with several antivirus partners and antimalware app developers to develop high-quality antimalware apps on
Windows 8 – some of which are now available for download.
Windows Defender is installed as a feature in Windows 8 and is enabled by default. But if you wish, you can use any other 3rd party anti-malware app to protect your computer. If you install one, Windows Defender will silently turn itself off.