TrueCrypt is free open-source, on-the-fly encryption for Windows. If you have data you want to secure on your computer, this is a free and secure way to do it. Some of the details follow:
On-the-fly encryption means that data are automatically encrypted or decrypted right before they are loaded or saved, without any user intervention. No data stored on an encrypted volume can be read (decrypted) without using the correct password/keyfile(s) or correct encryption keys. Entire file system is encrypted (e.g.., file names, folder names, contents of every file, free space, meta data, etc).
