Final answer:
The type of malware that can replicate itself and spread without user consent is a virus, which is different from a Trojan horse, rootkit, or backdoor.
Step-by-step explanation:
The type of malware that can copy itself and infect a computer without the user's consent or knowledge is a) virus. A virus attaches itself to executable files and spreads to other files and computers when these infected files are executed. Unlike a virus, a Trojan horse is a type of malware that disguises itself as legitimate software but can enable unauthorized access to the user's system. A rootkit is a software suite that allows for stealthy presence on the computer, often hiding other malware or itself from detection. A backdoor is a secret entryway into software, often created deliberately, which can be exploited by hackers to gain unauthorized access to information or systems.