What is encryption?
When you send an email and attachment to someone you want to be sure that no one other than the intended recipient can read it. Only one way to be sure - encrypt it.
There is always the possibility that someone intercepts your email and steals your private or sensitive data or message. Or someone plants a trojan on your computer to copy files from a remote location. Or a disgruntled employee steals sensitive data.
Encoding the contents of the email or files in such a way that hides its contents from outsiders is called encryption. The process of retrieving the content is called decryption. Encryption and decryption usually make use of a key, and the coding method is such that decryption can be performed only by knowing the proper key.
DriveCrypt - software from Secure Star
BestCrypt - software from Jetico
PGP - probably the most widely used encryption software