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 (i.e., file names, folder names, contents of every file, and free space).

• # Creates a virtual encrypted disk within a file and mounts it as a real disk.
• # 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.
• # Provides two levels of plausible deniability, in case an adversary forces you to reveal the password
• # Encryption algorithms: AES-256, Serpent, and Twofish. Mode of operation: XTS.

• * Faster booting when the system partition/drive is encrypted (typically by 10%). (Windows Vista/XP/2008/2003)
• * Other minor improvements. (Windows, Mac OS X, and Linux)
• * On computers with certain hardware configurations, resuming from hibernation failed when the system partition was encrypted. Note: If you encountered this problem, the content of RAM may have been saved unencrypted to the hibernation file. You can erase such data, for example, by decrypting the system partition/drive (select System > Permanently Decrypt System Partition/Drive) and then encrypting it again. (Windows Vista/XP/2008/2003)
• * Workaround for a bug in the BIOS of some Apple computers that prevented users from entering pre-boot authentication passwords and controlling the TrueCrypt Boot Loader. (Windows Vista/XP/2008/2003)
• * When the system partition/drive is decrypted under Windows, the original partition table will not be restored. Note: This issue affected users who repartitioned an encrypted system drive and then decrypted it under Windows. (Windows Vista/XP/2008/2003)
• * Other minor bug fixes. (Windows, Mac OS X, and Linux)