What is Trojan)?

Trojan

Trojans and backdoors are two ways a hacker can gain access to
a target system. They come in many different varieties, but they
all have one thing in common: They must be installed by another
program, or the user must be tricked into installing the Trojan or backdoor on their system.
Trojans and backdoors are potentially harmful tools in the ethical hacker’s toolkit and should
be used judiciously to test the security of a system or network.