From the How to Upgrade dept.:
The Lightweight Portable Security distribution was created by the Software Protection Initiative under the direction of the Air Force Research Laboratory and the U.S. Department Of Defense. The idea behind it is that government workers can use a CD-ROM or USB stick to boot into a tamper proof, pristine desktop when using insecure computers such as those available in hotels or a worker's own home. The environment that it offers should be largely resistant to Internet-borne security threats such as viruses and spyware, particularly when launched from read-only media such as a CDROM. The LPS system does not mount the hard drive of the host machine, so leaves no trace of the user's activities behind.