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Keeping the number of incidents reasonably low is very important to protect the business processes of the organization. If security controls are insufficient, higher volumes of incidents may occur, overwhelming the incident response team. This can lead to slow and incomplete responses, which translate to a larger negative business impact (e.g., more extensive damage, longer periods of service, and data unavailability). It is outside the scope of this document to provide specific advice on securing networks, systems, and applications. Although incident response teams are generally not responsible for securing resources, they can be advocates of sound security practices. An incident response team may be able to identify problems that the organization is otherwise not aware of; the team can play a key role in risk assessment and training by identifying gaps. Other documents already provide advice on general security concepts and operating system and application-specific guidelines. The following text, however, provides a brief overview of some of the main recommended practices for securing networks, systems, and applications:

Risk Assessments. Periodic risk assessments of systems and applications should determine what risks are posed by combinations of threats and vulnerabilities. This should include understanding the applicable threats, including organization-specific threats. Each risk should be prioritized, and the risks can be mitigated, transferred, or accepted until a reasonable overall level of risk is reached. Another benefit of conducting risk assessments regularly is that critical resources are identified,  allowing staff to emphasize monitoring and response activities for those resources.

Host Security. All hosts should be hardened appropriately using standard configurations. In addition to keeping each host properly patched, hosts should be configured to follow the principle of least privilege—granting users only the privileges necessary for performing their authorized tasks. Hosts should have auditing enabled and should log significant security-related events. The security of hosts and their configurations should be continuously monitored. Many organizations use Security Content Automation Protocol (SCAP) expressed operating system and application configuration checklists to assist in securing hosts consistently and effectively.

Network Security. The network perimeter should be configured to deny all activity that is not expressly permitted. This includes securing all connection points, such as virtual private networks (VPNs) and dedicated connections to other organizations.

Malware Prevention. Software to detect and stop malware should be deployed throughout the organization. Malware protection should be deployed at the host level (e.g., server and workstation operating systems), the application server level (e.g., email server, web proxies), and the application client level (e.g., email clients, instant messaging clients).

User Awareness and Training. Users should be made aware of policies and procedures regarding the appropriate use of networks, systems, and applications. Applicable lessons learned from previous incidents should also be shared with users so they can see how their actions could affect the organization. Improving user awareness regarding incidents should reduce the frequency of incidents. IT staff should be trained so that they can maintain their networks, systems, and applications in accordance with the organization’s security standards.


Incidents can occur in countless ways, so it is infeasible to develop step-by-step instructions for handling every incident. Organizations should be generally prepared to handle any incident but should focus on being prepared to handle incidents that use common attack vectors. Different types of incidents merit different response strategies. The attack vectors listed below are not intended to provide a definitive classification for incidents; rather, they simply list common methods of attack, which can be used as a basis for defining more specific handling procedures.

External/Removable Media. An attack executed from removable media or a peripheral device—for example, malicious code spreading onto a system from an infected USB flash drive.

Attrition. An attack that employs brute force methods to compromise, degrade, or destroy systems, networks, or services (e.g., a DDoS intended to impair or deny access to a service or application; a brute force attack against an authentication mechanism, such as passwords, CAPTCHAS, or digital signatures). 

Web. An attack executed from a website or web-based application—for example, a cross-site scripting attack used to steal credentials or redirect to a site that exploits a browser vulnerability and installs malware.

Email. An attack executed via an email message or attachment—for example, exploit code disguised as an attached document or a link to a malicious website in the body of an email message.

Impersonation. An attack involving the replacement of something benign with something malicious— for example, spoofing, a man in the middle attacks, rogue wireless access points, and SQL injection attacks all involve impersonation.

Improper Usage. Any incident resulting from a violation of an organization’s acceptable usage policies by an authorized user, excluding the above categories; for example, a user installs file-sharing software, leading to the loss of sensitive data; or a user performs illegal activities on a system.

Loss or Theft of Equipment. The loss or theft of a computing device or media used by the organization, such as a laptop, smartphone, or authentication token.

Other. An attack that does not fit into any of the other categories. 

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