There are many free tools to encrypt sensitive data. Most of them let you encrypt an entire drive (e.g., Windows Vista's built-in feature) or create and encrypt a virtual drive (e.g., TrueCrypt). However, when you copy a file to removable media, the file isn't encrypted anymore. To avoid this situation, I use Axantum Software's AxCrypt. You can use this free utility to encrypt a single file or a group of files. It remembers the file extension, so you can open the file later with a double-click.
AxCrypt integrates with Windows Explorer, so the easiest way to encrypt a file is to right-click it and select Encrypt from the AxCrypt context menu. When you encrypt your first file, you'll be asked to enter and verify a passphrase. If you select the Use as default for encryption check box, you won't have to enter a passphrase when encrypting other files during that session. After you click OK, the file is compressed, encrypted, and renamed using the format Filename-Extension.axx, where Filename is the file's original name and Extension is its original extension. For example, a file named My review.doc will be encrypted and renamed My review-doc.axx.
The AxCrypt context menu offers other options, including:
- Encrypt a copy: Makes a copy of a file, then compresses and encrypts the copy.
- Encrypt copy to .EXE: Creates self-decrypting .exe files that you can send to users who don't have AxCrypt installed.
- Shred and Delete: Overwrites a file's contents with random data, then deletes it. You can even use this option on files that aren't encrypted.
- Clear Passphrase Memory: Clears the passphrases from memory immediately, without waiting for logoff or reboot.
AxCrypt works on Windows 2000 and later. It can be used with files stored within a TrueCrypt volume for double protection.