‘Qubes is an open source operating system based on Linux, which is designed to provide strong security for desktop computing. Its unique selling point is that all applications that are run on Qubes is sand-boxed from each other.

This is achieved by way of virtualization of all applications using Xen Hypervisor.

Computer systems usually provide OS security in three basic ways, namely -

1. Security by correctness,
2. Security by obscurity, and
3. Security by isolation.

Qubes OS developers have embraced the path of security by isolation. To do this Qubes utilizes virtualization technology to isolate various programs from each other. This makes Qubes OS a secure by default operating system.

The idea is that virtual machines will be created on demand, for each application and discarded after use. Industry pundits have coined a new name for it – Disposable Virtual Machine technology.’linuxhelp.blogspot.com