Which type of attack is characterized by using intermediary computers to send requests to a victim?

The type of attack characterized by using intermediary computers to send requests to a victim is a distributed denial-of-service (DDoS) attack. In this approach, multiple compromised computers, often part of a botnet, are used to flood a target with a large volume of traffic. This overwhelming influx can render the target system or network unable to handle legitimate requests, leading to downtime or degradation of service.

A DDoS attack is particularly threatening because it can originate from numerous sources simultaneously, making it difficult for the victim to mitigate the attack effectively. The sheer scale and distributed nature of this attack method contribute to its effectiveness against even well-protected networks and servers.

The other types of attacks listed do not involve the same use of intermediary systems to direct traffic in the manner DDoS does. For example, a denial-of-service (DoS) attack typically comes from a single source, while man-in-the-middle attacks focus on intercepting and manipulating communications rather than overwhelming a target with requests. Polymorphic viruses are programs that evolve to avoid detection, rather than directly instigating a traffic flood.