TrueCrypt

TrueCrypt is a software system for establishing and maintaining an on-the-fly-encrypted drive. On-the-fly encryption means that data are automatically encrypted or decrypted right before they are loaded or saved, without any user intervention. No data stored on an encrypted volume can be read (decrypted) without using the correct password or correct encryption key. Until decrypted, a TrueCrypt volume appears to be nothing more than a series of random numbers.

The entire file system is encrypted ( file names, folder names, contents of every file, and free space). This software is highly recommended for securing data on laptops.

Features:
Ability to encrypt a non-system partition without losing existing data on the partition.
Encrypts an entire partition or storage device such as USB flash drive or hard drive.
Encrypts a partition or drive where Windows is installed (pre-boot authentication).
Encryption is automatic, real-time (on-the-fly) and transparent.
Creates a virtual encrypted disk within a file and mounts it as a real disk.
Support for security tokens and smart cards

During the process of creation of a hidden operating system, TrueCrypt now securely erases the entire content of the partition where the original system resides after the hidden system has been created. The user is then prompted to install a new system on the partition and encrypt it using TrueCrypt (thus the decoy system is created).

Protection against memory corruption caused by bugs in certain versions of some BIOSes, which prevented the TrueCrypt boot loader from working properly. (Windows Vista/XP/2008/2003)