TrueCrypt - Free Open-Source On-The-Fly Disk Encryption Software for Windows Vista/XP/2000 and Linux
T r u e C r y p t
Free open-source disk encryption software for Windows Vista/XP/2000 and Linux
Main Features:
- Creates a virtual encrypted disk within a file and mounts it as a real disk.
 - Encrypts an entire hard disk partition or a storage device such as USB flash drive.
 - Encryption is automatic, real-time (on-the-fly) and transparent.
 - Provides two levels of plausible deniability, in case an adversary forces you to reveal the password:
1) Hidden volume (steganography – more information may be found here).
2) No TrueCrypt volume can be identified (volumes cannot be distinguished from random data). - Encryption algorithms: AES-256, Serpent, and Twofish. Mode of operation: LRW.  
Further information regarding features of the software may be found in the documentation.
 
What is new in TrueCrypt 4.3a   (released May 3, 2007)