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.
BullGuard, F-Secure, Kaspersky, McAfee, Panda, Norton and Trend Micro have already made their anti-malware apps available for Widows 8 Release Preview.
Make sure you install only one anti-malware app, as it can cause problems on your PC if have two or more anti-malware apps enabled at the same time.
You may also want to avoid installing any other so-called security apps. It’s best to install them only from genuine sources.
Visit Microsoft to see the download links.