... If you don’t have another solution installed, Windows 8 will provide you protection with a significantly improved version of Windows Defender.
Improved protection for all types of malware.
The improvements to Windows Defender will help protect you from all types of malware, including viruses, worms, bots and rootkits by using the complete set of malware signatures from the Microsoft Malware Protection Center
, which Windows Update will deliver regularly along with the latest Microsoft antimalware engine
. This expanded set of signatures is a significant improvement over previous versions, which only included signatures for spyware, adware, and potentially unwanted software.
In addition, Windows Defender will now provide you with real-time detection and protection from malware threats using a file system filter, and will interface with Windows secured boot, another new Window 8 protection feature.
... In conclusion, we’ve taken a very broad approach to improving the level of protection you’ll get from malware in Windows 8, including the use of SDL processes to be secure by design, the implementation and upgrading of mitigations to help protect you against exploits used by malware, improvements to Windows Defender to provide you with real-time protection against all categories of malware, and the use of URL and application reputation to help protect you against social engineering attacks.