John, a disgruntled ex-employee of an organization, contacted a professional hacker to exploit the organization. In the attack process, the professional hacker Installed a scanner on a machine belongi

A proxy scanner typically intercepts and analyzes web traffic between a client and a server to find web application vulnerabilities; it's not installed on a target machine to scan other network machines.

An agent-based scanner operates by deploying a software agent directly onto the target machine, which then performs scans locally and reports back to a central console. In this scenario, the hacker 'installed a scanner on a machine belonging to one of the victims and scanned several machines on the same network,' indicating that the scanning capability was executed from a local agent on a compromised host within the network.

A network-based scanner operates remotely over the network, scanning target hosts without requiring direct installation of software on the target itself, which contradicts the scenario where a scanner was 'installed on a machine'.

The term 'cluster scanner' is not a standard or widely recognized type of vulnerability assessment tool in this context; it might refer to scanning a cluster of machines but doesn't describe the deployment method.