TrueCrypt is an open-source encryption software that enables you to create a virtual encrypted disk within a file and mount it as a virtual disk, that can be accessed via a drive letter. Any file that is stored on this virtual drive is automatically encrypted on-the-fly, and can only be accessed while the drive is mounted with the correct password or key. TrueCrypt supports a variety of encryption algorithms, including AES-256, Blowfish (448-bit key), CAST5, Serpent, Triple DES, and Twofish. Other features include support for FAT32 or NTFS formatting, hidden volumes, hotkeys for mounting/dismounting and more.