Whonix: Anonymous Operating System
sourceforge.net
Taken from Whonix home page:
Whonix is an anonymous general purpose operating system based on Virtual Box, Debian GNU/Linux and Tor. By Whonix design, IP and DNS leaks are impossible. Not even malware with root rights can find out the user's real IP/location.
This is because Whonix consists of two (virtual) machines. One machine solely runs Tor and acts as a gateway, which we call Whonix-Gateway. The other machine, which we call Whonix-Workstation, is on a completely isolated network. Only connections through Tor are possible.