Reimaging the systems (B) is the most reliable method to eradicate malware because it ensures complete removal of malicious code, including hidden persistence mechanisms. Malware scanning (A) may miss advanced threats, while blocking access (C) is a containment action, not eradication. Vulnerability assessments (D) help identify weaknesses but do not remove existing malware. CISM incident management guidance prioritizes thorough eradication to prevent reinfection and restore system integrity. References: ISACA CISM Review Manual (Incident management-eradication strategies); CISM Exam Content Outline (Domain 4).