TrueCrypt http://www.truecrypt.org/ Free open-source disk encryption software for Windows XP/2000/2003 and Linux Main Features: --It can create a virtual encrypted disk within a file and mount it as a real disk. --It can encrypt an entire hard disk partition or a device, such as USB memory stick, floppy disk, etc. --Provides two levels of plausible deniability, in case an adversary forces you to reveal the password: 1) Hidden volume (more information may be found here). 2) No TrueCrypt volume can be identified (TrueCrypt volumes cannot be distinguished from random data). --Encryption algorithms: AES-256, Blowfish (448-bit key), CAST5, Serpent (256-bit key), Triple DES, and Twofish (256-bit key). Supports cascading (e.g., AES-Twofish-Serpent). --Based on Encryption for the Masses (E4M) 2.02a, which was conceived in 1997. Lots of major improvements including addition of whirlpool hash algo as alternative to SHA-1 (plus ability to reencrypt existing header volumes) , using of keyfiles to supplement passwords (plus ability to add these to existing volumes), improved automount and dismount features, backup/replacement of header volumes, protection of hidden volume, improved to speed and RNG.