Rather than being impregnable fortresses of steel, most computers are about as leaky as old wooden fishing boats. Though the press has focused primarily on Windows security violations in the last few years, Unix boxes are just as vulnerable and require as much, or more, effort to keep safe.
If your Unix box sits in your home, it is protected from unauthorized access, you live alone, and you never connect to the Internet, security probably isn’t a concern for you. However, chances are your Unix box is fairly easy to access physically, and your system is most likely connected to the Internet through a modem or other network connection. In both these cases, this chapter and those that follow are of extreme interest to you.
Anytime you have a multiuser system, your account is vulnerable to others in the system and to anyone who might break into the system from outside your organization. The only way to protect accounts is to ensure that good account management practices are in place, such as removing accounts when people are no longer with the organization and using difficult-to-hack passwords, as well as making sure that sensitive data is protected by accidental or deliberate access.
For single-user systems, you’ll want to make sure that someone can’t accidentally or deliberately log into your machine at home or work. Chances are no one would try, but particularly if you have something such as Linux installed on a laptop, ...