Final answer:
Changing the default administrator account should generate an alert when an account is disabled or altered, as it's a significant change affecting a highly privileged account.
Step-by-step explanation:
The action that should generate an alert when an account is disabled or altered is a. Change default administrator account. In the context of IT security, alerts are often configured to notify system administrators or security systems when critical changes occur that might impact the security posture of the system. Changing the default administrator account is a significant alteration since it involves one of the highest privileged accounts on a system. Therefore, altering this account should trigger an alert to ensure any changes are monitored and verified as legitimate. In contrast, enabling a guest account, disabling User Account Control (UAC), and setting a weak password, while not best practices, are not actions that directly involve disabling or altering critical accounts in such a way that a default security system would alert an administrator.