It can cause havoc by multiplying so many times that take up all the computer's available memory are called

A computer worm is a standalone malware program that replicates itself in order to spread to other computers, often consuming immense amounts of system memory or network bandwidth in the process. Unlike Trojans, which rely on tricking users into running them, or spyware, which quietly steals data, worms are characterized by their self-replicating and resource-consuming nature.