"If you want to encrypt your sensitive files so that no one can access them without your personal password or decryption key, you have several options. But if you want a free, cross-platform, open source encryption application, try TrueCrypt.
"TrueCrypt encrypts and decrypts files on the fly, as they are loaded or saved, without user intervention. TrueCrypt can encrypt files and store them in a container file that acts as a virtual disk, or make an entire partitions or disk into an encrypted volume in both Microsoft and Linux. The software depends on a personal password or key that you create when configuring a TrueCrypt volume. Without this key, no data on an encrypted volume can be read (not even offline)..."
