The glossary below contains many of the terms you will find in common use throughout our website. Please refer to this list to find definitions of terms and answers to other Internet security-related questions.


A backdoor is a type of malicious code that, once installed on a system, allows attackers to bypass normal security access controls and access the system.

Also called a trapdoor. An undocumented way of gaining access to a program, online service, or an entire computer system. A programmer who creates a threat program writes the code for a backdoor, as well. Often only the programmer knows the backdoor details. A backdoor is a potential security risk.