free encryption software
TrueCrypt is encryption software: it can keep your files from being accessed unless the correct password/keyfile(s), or encryption keys, are used.
TrueCrypt will hide operating systems, also!
BEFORE USING THE SOFTWARE, I strongly recommend you at least browse through the TrueCrypt User’s Guide. It is included in the download, and available to you after you execute the file you downloaded. It is best that, before you use TrueCrypt, you become familiar with: some of the terms, what the software will do and how it will perform, and where you can refer to if you have a question. The Beginner's Tutorial chapter can be viewed at http://www.truecrypt.org/docs/tutorial.php
[One of those terms you will need to be familiar with: a TrueCrypt volume is also known as a "container", a file that contains the encrypted files.]
After you download the setup file (from http://www.truecrypt.org/downloads.php), and execute it, you are offered to: "install" it, or to "extract" it. If you choose "extract", you can save the files to a folder...and carry and use it on an external drive. This is a version of "traveler" mode (which can also be used if TrueCrypt is installed to an operating system).
The User's Guide states that there are two ways to run TrueCrypt in ‘traveler’ mode:
1) After you unpack the binary distribution archive (what you downloaded), you can directly run TrueCrypt.exe.
2) You can use the Traveler Disk Setup facility to prepare a special "traveler" disk, and launch TrueCrypt from there.
You will need to create a TrueCrypt file container on the USB flash drive (see the Beginner’s Tutorial), so...
Before you use TrueCrypt on a USB flash drive, know that:
1) If you encrypt the entire USB flash drive, you will not be able run TrueCrypt from the USB flash drive.
2) Before you choose the size for the TrueCrypt container on a USB drive, if you leave enough space on the USB flash drive for TrueCrypt (not IN the "container" file - along WITH the "container" file), you will be able to run TrueCrypt from the USB flash drive (see the Traveler Mode chapter in the User's Guide).
It is not difficult to use...do not fear trying it to see if it will work for your security needs.