Backdoor, Remote Access Tool/Remote Access Trojan (RAT)
A backdoor is an application allowing remote access to a computer. The difference between this type of malware and a legitimate application with similar functionality is that the installation is done without the user’s knowledge.
Typical backdoor functionality includes the capability to send files to the host computer and execute files and commands on it, and to exfiltrate (send) files and documents back to the attacker. Often this is coupled with key-logging and screen-grabbing functionality for purposes of spying and data theft.
The term “RAT” (Remote Access Tool) can be considered a synonym to “backdoor”, but it usually signifies a full bundle including a client application meant for installation on the target system, and a server component that allows administration and control of the individual ‘bots’ or compromised systems.