Tails stands for The Amnesic Incognito Live System. It is a live operating system that aims to preserve your privacy and anonymity. Tails is intended to be booted off of a live CD and leave no trace on the computer it is run on, but using Tails this way requires the user to restart their computer every time they want to switch from their installed OS to Tails. Despite this, in case that method becomes cumbersome, Tails can be used inside virtualization software and Qubes.
To run Tails under Qubes:
Read about creating and using HVM qubes
Download and verify Tails from https://tails.boum.org in a qube, (saved as /home/user/Downloads/tails.iso on qube "isoVM" for purposes of this guide).
Create a HVM
Open dom0 Konsole and start Tails:
qvm-start Tails --cdrom=isoVM:/home/user/Downloads/tails.iso
Configure Tails at start up.
Once the Tails qube has started, configure networking in the qube.
qvm-ls -n Tails in Konsole. (E.g. 10.137.1.101 with gateway 10.137.1.1)10.137.1.101 in our example.255.255.255.010.137.1.1 in our example.10.137.1.1 in our example.Use Tails as normal.
You will probably want to implement MAC spoofing.
There are added security concerns for Tails users when running it in a virtual machine. If you intend to do this, you should read the warnings from the Tails team about it. While the Qubes security model mitigates most of the risks identified, traces of the Tails session may remain on the disk. Live booting Tails, though less convenient, is always more secure than using it inside virtualization software or Qubes, because you don't run the added risk of the virtualization software or Host OS being compromised. Depending on your threat model, this might induce too much risk.
See the Tails Troubleshooting guide.