You install Windows 8.
You change the Hosts file by specifying custom IP-address-to-host-name
mappings to prevent users from browsing to some websites.
You run a scan in Microsoft Windows Defender.

In this scenario, the Hosts file is detected as a
SettingsModifier:Win32/PossibleHostsFileHijack by Windows Defender.

Source: http://msmvps.com/blogs/siljaline/default.aspx