If you would like to keep all your files or folders secured, you can try out TrueCrypt. It is a free open-source disk encryption software that can be installed on almost all operating systems out there i.e. Windows 7, Vista/XP, Mac OS X, and Linux Main.

Basically. TrueCrypt protects users by offering powerful data protection, recommending complex passwords, explaining the benefits of hidden volumes, and erasing telltale signs of the encryption process, including mouse movements and keystrokes

Main Features of TrueCrypt are:

• Creates a virtual encrypted disk within a file and mounts it as a real disk.
• Encrypts an entire partition or storage device such as USB flash drive or hard drive.
• Encrypts a partition or drive where Windows is installed (pre-boot authentication).
• Encryption is automatic, real-time (on-the-fly) and transparent.
• Parallelization and pipelining allow data to be read and written as fast as if the drive was not encrypted.
• Provides plausible deniability, in case an adversary forces you to reveal the password:
  Hidden volume (steganography) and hidden operating system.
• Encryption algorithms: AES-256, Serpent, and Twofish.

Download TrueCrypt from here.