TrueCrypt — Learn the Art of Encryption
Many commercial encryption products can protect files, folders and partitions. Probably the most discussed is “Bitlocker”, which is bundled free with MS Windows 7 Ultimate. And if you have ever wondered if there is open source encryption software — there is and it’s called TrueCrypt.
As mentioned on TrueCrypt.org, it is a software system to establish and maintain an on-the-fly-encrypted volume (data storage device). On-the-fly implies that data is automatically encrypted right before it is saved, and decrypted right after it is read, without user intervention. No data stored on an encrypted volume can be decrypted without the correct password/keyfile(s) or correct encryption keys. The entire file system is encrypted.
Files can be copied to and from a mounted TrueCrypt volume just like with any normal disk (for example, by simple drag-and-drop operations). The software works as expected, is simple, and has a GUI for ease of use.