Microsoft plan to make its Operating System a secured OS by including a inbuilt antivirus on Windows 8.This will protect windows from affected by spyware,virus & spams.They will provide it at a free of cost but it is only for few days after that it will be available as windows update.Those who have not any installed antivirus they can use it.
Windows provide this facility at free of cost,they are providing Microsoft Windows Essential as the antivirus.This service is available with windows defender.It will work like antivirus to protect windows from virus,spyware etc.
According to Microsoft if you boot windows 8 with a virus infected USB device then windows 8 automatically reject this booting device.It is both restricted for Internet Explorer and other installed browsers.This is planned to make a secure operating system to Microsoft’s users.For more read on here.