Investigating the credentials and recent activity of the administrator account that created the new accounts is the best step to determine if this action is legitimate or malicious. Usually, an account that does not typically perform these actions but suddenly creates multiple new accounts is indicative of compromised credentials or insider threat. Reviewing the time of creation, IP address, and access patterns can reveal anomalies or confirm authorized activity. Disabling the new accounts does not address the potential root cause and can disrupt legitimate operations if the accounts are valid. Analyzing prior threat intelligence might assist in a broader context but does not directly relate to the immediate incident. Finally, increasing network bandwidth would not be useful in this situation and does not address the creation of new accounts.