Which term describes software that replicates to infect multiple computers, turning them into "zombies"?

The term that describes software designed to replicate itself and infect multiple computers, effectively turning them into "zombies," is botnet. A botnet consists of a network of compromised computers, often referred to as "bots" or "zombies," which can be remotely controlled by an attacker. These compromised machines perform various malicious tasks, such as sending spam emails, distributing malware, or launching distributed denial-of-service (DDoS) attacks. The key aspect of a botnet is its ability to propagate and maintain control over a large number of infected devices, transforming them into a coordinated network for malicious purposes.

Other terms listed refer to different types of malicious software or techniques: a rootkit is used to gain unauthorized access and hide the presence of something malicious, a keylogger records keystrokes to capture sensitive information like passwords, and ransomware encrypts a victim's data and demands a ransom to restore access. Each serves distinct roles in cybersecurity threats, but none fulfill the criteria of self-replicating and creating "zombie" systems like a botnet does.