The guideline that helps incident handlers to eradicate insider attacks by privileged users is to ensure accountability by not enabling default administrative accounts. Instead, organizations should require administrators and privileged users to use individual accounts that can be audited and traced back to specific actions and users. This practice enhances security by ensuring that all actions taken on the system can be attributed to individual users, reducing the risk of misuse of privileges and making it easier to identify the source of malicious activities or policy violations. The other options listed either present insecure practices or misunderstandings of security protocols that would not help in eradicating insider attacks.