The most effective response to a hacker who has already gained access to a network and will attempt to pivot to other resources is to segment the network. Network segmentation is a technique that divides the network into smaller and isolated subnetworks, or segments, based on criteria such as function, location, or security level. Network segmentation can limit the impact and spread of a hacker's attack, by restricting the access and communication between the segments, and enforcing the security policies and controls for each segment.
Network segmentation can also help to detect and contain the hacker, by monitoring and analyzing the network traffic and activity between the segments, and isolating the compromised or suspicious segments. The other options are not as effective as segmenting the network, as they either do not address the hacker's attack, do not prevent the hacker from pivoting, or do not mitigate the impact of the attack. References: CISSP - Certified Information Systems Security Professional, Domain 4. Communication and Network Security, 4.1 Implement secure design principles in network architectures, 4.1.1 Apply secure design principles to network architecture, 4.1.1.2 Secure network design elements; CISSP Exam Outline, Domain 4. Communication and Network Security, 4.1 Implement secure design principles in network architectures, 4.1.1 Apply secure design principles to network architecture, 4.1.1.2 Secure network design elements