Practical Unix & Internet Security, 3rd Edition

An ounce of prevention . . .

The worst time to think about how to protect your computer and its data from intruders is after a break-in. At that point, the damage has already been done, and determining where and to what extent your system has been hurt can be difficult.

Did the intruder modify any system programs? Did the intruder create any new accounts, or change the passwords of any of your users? If you haven't prepared in advance, you could have no way of knowing the answers.

This chapter describes the ways in which an attacker can gain entry to your system through accounts that are already in place, and the ways in which you can make these accounts more difficult to attack.