Security applications programs are designed to protect computer files, operating systems, and program software, particularly on computers that are connected to networks or are otherwise subject to attack from outside locations. Security programs may be designed to detect the effects of intrusive activity, identify intrusive activity while it is occurring, look for vulnerabilities that might be exploited by an intruder, or help prevent intrusive activity.

Intrusive activity can take place directly, as in the case of an unauthorized user sitting down at an unattended computer and taking some action that affects the data, system, or program software in some way. More commonly, however, computer intruders gain unauthorized access through network or online connections. An intruder may alter programs or data contained in the computer, either as an end in itself or to allow future break-ins. An intruder may also install processes on the attacked...