TrueCrypt is a free software that encrypts data “on-the-flyâ€. Right now the newest version released is version 4.3. You can create an encrypted hard drive, a separate partition or a directory with TrueCrypt. It doesn’t encrypt simply the content of files but their names and the names of the directories they are in as well. Moreover there is no way to check the size of the encrypted directory/HDD/partition. TrueCrypt is available for Windows and Linux.
TrueCrypt is great software and worth consideration for anyone who is wanting to protect their data. This is a thorough tutorial, so you will not be left confused.
Source: Polish Linux