Thanks to the guest account, I now had access to one computer, which turned out to be running an older version of the UNIX operating system. Under UNIX, the operating system maintains a password file which contains the encrypted passwords of everybody authorized to access that computer. The password file contains the one-way hash (that is, a form of encryption that is irreversible) of every user's password. With a one-way hash an actual password such as, say, "justdoit" would be represented by a hash in encrypted form; in this case the hash would be converted by UNIX to thirteen alphanumeric characters.