Correct Answer. C. Conduct a security audit to identify and address any vulnerabilities A security audit helps to comprehensively assess and mitigate risks associated with unauthorized access attempts, identifying potential weaknesses in the system's security posture.
Option A is incorrect as ceasing all account usage is impractical and may hinder business operations.
Option B is incorrect because updating antivirus software, while important, does not directly address unauthorized access to accounts.
Option D is incorrect because merely using complex passwords is insufficient without a broader security review and response plan.