In which of the following does an attacker use multiple computers throughout the network that has been previously infected?

Phishing is a social engineering attack that tricks users into divulging credentials or executing malicious links via deceptive emails or websites, and involves no network of infected machines.

In a DDoS attack, an attacker coordinates a botnet - a large collection of hosts that were previously compromised with malware - to simultaneously send overwhelming volumes of traffic or requests to a target system or network. The distributed nature across many infected machines makes the attack far more powerful than a single-source DoS and significantly harder for defenders to block by filtering one IP address.

A DoS (Denial of Service) attack originates from a single machine controlled by the attacker, not from multiple distributed previously infected hosts.

A sniffer is a passive packet-capture tool used to intercept and inspect network traffic and is not an attack that leverages infected computers.