Protect your sensitive data with this free open-source disk encryption software. Creates a virtual encrypted disk within a file and mount it as a real disk. Encrypt an entire hard disk partition or a device, such as USB flash drive. Automatically and transparently encrypt in real time.

TrueCrypt provides two levels of plausible deniability, in case an adversary forces you to reveal the password: a hidden volume (steganography- more information may be found here); no TrueCrypt volume can be identified (volumes cannot be distinguished from random data). TrueCrypt uses encryption algorithms AES-256, Blowfish (448-bit key), CAST5, Serpent, Triple DES, and Twofish. It is based on Encryption for the Masses (E4M) 2.02a, conceived in 1997.

Editor's review of TrueCrypt Ssshhh

This open-source encryption program is loaded with powerful encryption features, but a lack of in-program help may dissuade all but those users who definitely need or want to completely secure their data. A powerhouse of potential, TrueCrypt offers 11 algorithms for encrypting your private files in a password-protected volume. You can store your encrypted data in files (containers) or partitions (devices). TrueCrypt works hard to offer powerful data protection, recommending complex passwords, explaining the benefits of hidden volumes, and erasing telltale signs of the encryption process, including mouse movements and keystrokes. Though the interface may not be immediately intuitive, its powerful, on-the-fly encryption for no cost still earns the freeware security tool a top rating.

The useful tips in the extensive help manual and volume-creation wizard provide excellent guidance. In fact, they're rather required reading, as TrueCrypt lacks any considerable in-program help. For instance, the tutorial explains the entire concept beyond "hidden" volumes, but it doesn't quite explain how to mount them. One obvious downside of any strong encryption program is if you happen to forget your lengthy, secure password, you should consider any protected files as good as gone. However, once files are mounted to a local drive with your password or key, they conveniently behave just like any normal files, allowing you to easily open, copy, delete, or other modify them. Dismount the volume, and voila--your previously accessible files are now safely secure from prying eyes.