A(n) is a harmful program that resides in the active memory of the computer and duplicates itself.
worm
virus
keylogger
timebomb

Worm

Explanation: Worm is the malicious software program which acts as the infection in the computer system. It has the ability to replicate itself and spread in the other systems .It is found in those parts that have automatic operation and non-noticeable.

The effect of the worm is slowing down the operations ,disturb the network etc.Other options are incorrect because virus is the malicious program that infects the host, key-loggers are used for monitoring of system and  time bomb is the program for releasing the virus in computer network. Thus, the correct option is worm.

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