Backdoor

A backdoor is a secret passage to gain access to a computer program, an online service, a computer network or a computer. The backdoor is the opposite of the standard access, the front door.

A bacdoor can be created intentionally by the programmer for e.g maintenace purposes or to get access in an emergency situation. Backdoors can also be unintentionally "created" by flaws in a computer program.

Hackers exploite backdoors to gain unoffical access to a system. Backdoors are also used by virusses and spyware.