TrueCrypt is a disk-encryption software. Typically, data stored in the hard drive is not encrypted, which means if your hard disk or USB drive has been stolen, all data files inside will be in high risk. TrueCrypt provides several methods to encrypt data before storing in the hard disk. Once TrueCrypt is setup properly, you can use Windows Explorer to manage your files as usual, it is because TrueCrypt will handle the encryption and decryption process on-the-fly.