Pretty Good Privacy (PGP) is a popular program that is used to encrypt and decrypt email and files. It also provides the ability to digitally sign a message so the receiver can be certain of the sender’s identity. Taken together, encrypting and signing a message allows the receiver to be assured of who sent the message and to know that it was not modified during transmission. Public domain versions of PGP have been available for years as well as inexpensive commercial versions. PGP is one of the most widely used programs and is frequently used by both individuals and businesses to ensure data and e-mail privacy. It was developed by Philip R. Zimmermann in 1991 and quickly became a de facto standard for e-mail security.