Backdoor
Security hole allowing remote control
A backdoor is a piece of software which, once running on a system, opens a communication vector to the outside so that the computer can be accessed remotely by an attacker.
Backdoors are usually trojans and may be dropped by or included within some worms and viruses. Backdoors can be used to gather sensitive data from the infected system, stealing personal information including login details for banks and other online services (using keyloggers), collecting email addresses for spamming, or they can be used to control botnets of zombies, sending spam or hosting malicious code.
