Explanation
The document that should be triggered first when unknown malware has infected an organization's critical system is the incident response plan because it defines the roles and responsibilities, procedures and protocols, tools and techniques for responding to and managing a security incident effectively and efficiently. Disaster recovery plan (DRP) is not a good document for this purpose because it focuses on restoring the organization's critical systems and operations after a major disruption or disaster, which may not be necessary or appropriate at this stage. Business continuity plan (BCP) is not a good document for this purpose because it focuses on restoring the organization's critical business functions and operations after a major disruption or disaster, which may not be necessary or appropriate at this stage. Vulnerability management plan is not a good document for this purpose because it focuses on identifying and evaluating the security weaknesses or exposures of the organization's systems and assets, which may not be relevant or helpful at this stage.
References:
https://www.isaca.org/resources/isaca-journal/issues/2017/volume-5/incident-response-lessons-learned
https://www.isaca.org/resources/isaca-journal/issues/2018/volume-3/incident-response-lessons-learned

Security baselines will provide the best assurance that each platform meets minimum criteria. Penetration testing will not be as effective and can only be performed periodically. Vendor default settings will not necessarily meet the criteria set by the security policies, while linking policies to an independent standard will not provide assurance that the platforms meet these levels of security.

Section: INFORMATION RISK MANAGEMENT
Explanation:
Risk analysis explores the degree to which an asset needs protecting so this can be managed effectively. Risk analysis indirectly supports the security expenditure, but justifying the security expenditure is not its primary purpose. Helping businesses prioritize the assets to be protected is an indirect benefit of risk analysis, but not its primary purpose. Informing executive management of residual risk value is not directly relevant.

The primary objective of a security review or audit should be to provide assurance on the adequacy of security controls. Reviews should focus on all forms of control, not just on preventive control. Cost-effectiveness and technological currency are important but not as critical.