Being a user on a UNIX system makes you a potential security hole. Do a couple of things to avoid becoming a cracker's way in.
First, choose a smart password. This means do not have all or part of your login name in your password; do not have your cat's name or your mother's maiden name or Mao's middle name in your password. Do not have any English words in your password. Do have at least 6 characters, at least one of which is non-alphanumeric (such as an ampersand or an equals sign or something). To keep you honest, there is a password cracking program which runs periodically. If it guesses your password it will disable your account.
Second, be careful about logging in as root. If possible, do so on the machine's console. Avoid using 'rlogin' to become superuser, and avoid sending a machine's root password through your modem.
In case you are wondering, SEP has had a major breakin. In the early 1990s, somebody managed to gain access and erase every file on the system. Of course, everything is backed up, and therein lies our real security; but it is tedious, annoying, and a little embarrassing to have to restore your system from tape.