Residual risk is the risk that remains after the risk mitigation plans have been implemented. Residual risk reflects the effectiveness of the risk response in reducing the likelihood or impact of the risk. The best evidence that risk mitigation plans have been implemented effectively is the change in the level of residual risk. A change in the level of residual risk can be measured by comparing the risk level before and after the risk mitigation plans have been executed. A change in the level of residual risk can also be evaluated by comparing the actual residual risk with the target or acceptable residual risk. A change in the level of residual risk can demonstrate how well the risk mitigation plans have achieved the risk objectives and met the risk criteria. A change in the level of residual risk can also provide feedback and lessons learned for future risk management activities. References = Residual Risk: Definition, Formula & Management, Residual Risk:
What It Is and How to Manage It, Residual Risk: How to Calculate and Manage It.

The second line of defense is a group of functions that provide oversight, guidance, and monitoring of the risk management activities of the first line of defense. The second line of defense includes risk management, compliance, and internal control departments. Their key responsibility is to monitor the effectiveness of the control activities implemented by the first line of defense, and to report any issues or gaps to senior management and the board. The second line of defense also supports the first line of defense by providing frameworks, policies, tools, and techniques to identify, measure, and manage risks. The other options are not the key responsibility of the second line of defense, as explained below:
* A. Implementing control activities is the responsibility of the first line of defense, which consists of the business units and process owners that own and manage the risks associated with their daily operations.
* C. Conducting control self-assessments is a technique used by the first line of defense to evaluate the design and operation of their own controls, and to identify and report any deficiencies or improvement opportunities.
* D. Owning risk scenarios is the responsibility of the first line of defense, which is accountable for the risks inherent in their business activities, and for developing and executing risk response strategies.
References = Modernizing The Three Lines of Defense Model | Deloitte US, The second line of defence: fit for purpose, not an uncomfortable fit | Knowledge | Linklaters, COSO's Take on the Three Lines of Defense | ERM - Enterprise Risk Management, Three Lines of Defense | Risk Management - Schneider Downs CPAs, What is the Three Lines of Defense Approach to Risk Management?

* A security incident handling process is a set of procedures and activities that aim to identify, analyze, contain, eradicate, recover from, and learn from security incidents that affect the confidentiality, integrity, or availability of information assets12.
* The maturity of a security incident handling process is the degree to which the process is defined, managed, measured, controlled, and improved, and the extent to which it meets the organization's objectives and expectations34.
* The best key performance indicator (KPI) to measure the maturity of a security incident handling process is the number of recurring security incidents, which is the frequency or rate of security incidents that are repeated or reoccur after being resolved or closed56.
* The number of recurring security incidents is the best KPI because it reflects the effectiveness and efficiency of the security incident handling process, and the ability of the process to prevent or reduce the recurrence of security incidents through root cause analysis, corrective actions, and continuous improvement56.
* The number of recurring security incidents is also the best KPI because it is directly related to the organization's objectives and expectations, such as minimizing the impact and cost of security incidents, enhancing the security posture and resilience of the organization, and complying with the relevant standards and regulations56.
* The other options are not the best KPIs, but rather possible metrics that may support or complement the measurement of the maturity of the security incident handling process. For example:
* The number of security incidents escalated to senior management is a metric that indicates the severity or complexity of security incidents, and the involvement or awareness of the senior management in the security incident handling process56. However, this metric does not measure the effectiveness or efficiency of the process, or the ability of the process to prevent or reduce security incidents56.
* The number of resolved security incidents is a metric that indicates the output or outcome of the security incident handling process, and the performance or productivity of the security incident handling team56. However, this metric does not measure the quality or sustainability of the resolution, or the ability of the process to prevent or reduce security incidents56.
* The number of newly identified security incidents is a metric that indicates the input or demand of the security incident handling process, and the capability or capacity of the security incident detection and identification mechanisms56. However, this metric does not measure the effectiveness or efficiency of the process, or the ability of the process to prevent or reduce security incidents56. References =
* 1: Computer Security Incident Handling Guide, NIST Special Publication 800-61, Revision 2, August
2012
* 2: ISO/IEC 27035:2016 Information technology - Security techniques - Information security incident management
* 3: Capability Maturity Model Integration (CMMI) for Services, Version 1.3, November 2010
* 4: COBIT 2019 Framework: Introduction and Methodology, ISACA, 2018
* 5: KPIs for Security Operations & Incident Response, SecurityScorecard Blog, June 7, 2021
* 6: Key Performance Indicators (KPIs) for Security Operations and Incident Response, DFLabs White Paper, 2018

A post-implementation RCSA is a process of verifying whether the risk treatment plan has been executed as intended and whether the residual risk is within the acceptable level. It involves testing the effectiveness of the controls that have been implemented to mitigate the risk and identifying any gaps or issues that need to be addressed. A BIA, the original risk response plan, and the training program and user awareness documentation are not sufficient to validate the effectiveness of the risk treatment plan, as they do not measure the actual performance of the controls or the residual risk.
References:
*ISACA, Risk IT Framework, 2nd Edition, 2019, p. 761
*ISACA, Risk and Information Systems Control Review Manual, 7th Edition, 2020, p. 2112

The best way to increase the chances of a successful delivery of a new application and to assure the business management that IT has a plan in place for early identification of potential issues is to include business management on a weekly risk and issues report. A risk and issues report is a document that summarizes the current status, progress, and challenges of the IT project, as well as the actions and resources needed to address them. A risk and issues report helps to communicate and align the expectations and objectives of the IT and business stakeholders, and to facilitate timely and effective decision-making and problem-solving. A risk and issues report also helps to monitor and control the project scope, schedule, budget, and quality, and to ensure that the project delivers the desired value and benefits to the organization. The other options are not as effective as including business management on a weekly risk and issues report, although they may be part of the IT project management process or outcomes. Implementing a release and deployment plan, conducting comprehensive regression testing, and developing enterprise-wide key risk indicators (KRIs) are all activities that can help to ensure the quality and reliability of the new application, but they do not necessarily involve the business management or provide assurance for the early identification of potential issues. References = Risk and Information Systems Control Study Manual, Chapter 5, Section 5.4.1, page 5-32.