Trojan horses are malicious software programs that disguise themselves as legitimate programs. They are used by hackers to gain access to a computer system and steal sensitive personal and financial information. There are several synonyms for Trojan horses, including backdoor, rootkit, virus, and worm. Each of these terms refers to a type of malicious software that is designed to infiltrate a computer system and cause damage. Backdoor refers to a software program that allows unauthorized access to a computer system. Rootkit is a type of malware that hides its presence from the user. Virus and worm are both types of malware that spread from one computer to another.