One of the most popular technologies used to implement public-key encryption today is called Pretty Good Privacy (PGP). PGP was invented in 1991 by Phil Zimmerman, who charged businesses for use of PGP but allowed individuals to use PGP at no cost. PGP is a set of software tools that can use several different encryption algorithms to perform public-key encryption. The PGP business was purchased by Network Associates in 1997 and sold back to the product's developers, who formed the PGP Corporation in 2002. Today, individuals can download free versions of PGP for personal use from the PGP International site Individuals can use PGP to encrypt their e-mail messages to protect them from being read if they are intercepted on the Internet. The Symantec (which bought the original PGP Corporation) site sells PGP licenses to businesses that want to use the technology to protect business communication activities.