A backdoor virus is a program that enters a computer system without being detected and runs in the background to open ports, allowing third parties to control the computer clandestinely. These backdoor viruses can pass themselves off as legitimate programs.
Backdoor viruses can compromise files and capture confidential information stored on the infected machine. They also allow hackers to run malicious software from the computer's Internet connection to launch other attacks. A backdoor virus is similar to a Trojan with the added threat that it exposes an infected system to unwanted remote access. Backdoor viruses first appeared as networked operating systems grew in popularity.