An online trading company discovers that a network attack has penetrated the firewall. What should be the information security manager's FIRST response?

Prioritizing the evaluation of business impact helps determine the severity of the incident, the resources required for response, and informs immediate decisions about containment and recovery, ensuring critical business functions are addressed first. Understanding the business impact dictates the urgency and scale of all subsequent incident response activities.

Examining logs to identify the attacker is part of the investigation phase, which typically follows initial assessment and containment, and is not the absolute first step.

Notifying regulatory agencies might be required, but it's usually done after the initial assessment of impact and potential containment, as the scope and details of the incident need to be understood first.

Implementing mitigating controls is part of the containment phase, which occurs after assessing the impact and understanding what exactly needs to be mitigated.