A backdoor is a security vulnerability in a computer system, such as a web server or home PC. It is a hidden way to access a system that bypasses typical authentication methods. The term may be used as a noun or an adjective, such as "backdoor hack" or "backdoor access."
Security holes can exist in operating systems and individual applications. Operating system vulnerabilities are the most serious because once a hacker gains system-level access, he may have full access to all programs and data on the system. Application security holes are also serious since they may allow hackers to view or alter data on a computer and may more difficult to detect.
Examples of malware that may facilitate backdoor access include:
In some cases, backdoor hacks are immediately apparent since they affect the functionality of the system. In other cases, they may go undetected for hours, days, or even months. Long-term access is especially problematic since it provides hackers extra time to access, alter, and download data. For this reason, servers often have monitoring software that checks for unrecognized processes running on the system. Most antivirus software runs similar security checks.
Backdoor Attacks vs Other Cyberattacks
A backdoor attack is the opposite of a brute force attack, which attempts to gain access to a system through the standard login interface. Backdoor access bypasses the typical username and password authentication and gains access to the underlying system.
Viruses and other malware are not considered backdoor hacks, but instead, they facilitate backdoor access. For example, a malware program may install a script that provides a hacker with admin access to the system, even after the malware has been removed. Hackers can also gain backdoor access through a command-line interface, using SSH or other text-based commands.