Which of the following attacks involves multiple compromised systems to attack a single target?

A brute force attack systematically attempts all possible combinations of credentials or encryption keys against a target, not a multi-system network flood.

A replay attack captures a valid authentication token or message and retransmits it to gain unauthorized access, which involves no compromised botnet.

A dictionary attack uses a precompiled wordlist to guess passwords or keys against an authentication system and is a single-source credential attack.

Distributed Denial-of-Service (DDoS) is defined as an attack in which multiple compromised hosts (bots) simultaneously direct traffic or requests at a single target, overwhelming it beyond its capacity to respond to legitimate users. The 'distributed' component - many sources, one target - is the precise technical definition that makes D correct.