On the Internet a number of encryption methods have been developed, the most famous one being the encryption technique called 'Pretty Good Privacy' (PGP), invented by Phil Zimmerman (for which he also incidentally served a custodial term). PGP is technically one of the best E-mail encryption tools around and is available free of charge on numerous File Transfer Protocol (FTP) sites on the Internet. PGP provides three levels of public key protection (User, Commercial, Military). The aim is to provide the ultimate secure environment through encryption, although some would claim that PGP has already achieved this aim. By comparison with commercial encryption tools -the latest and perhaps most controversial to date being the one proposed by the US government and known as the 'Clipper Chip', PGP has managed to provide a free and elegant solution to E-mail privacy on the Internet. This contrasts with claims on the Net, that the first level of Clipper's security was breached by hackers within two weeks of getting hold of the Chip. But intense preoccupation with freedom of expression on the Internet can at times create responses that are somewhat paradoxical if not unorthodox; for example, recently, two computer security experts developed a program called 'SATAN', designed to probe the security of a computer network system in order to detect its weaknesses, so that appropriate security measures could be implemented on the system. However, this program, fallen into the wrong hands, could also provide an effective tool for breaking into a computer hooked up by a potential hacker on the Internet.